Nine months before the Olympic Games in Rio de Janeiro, a small victory in the epic fight against the dark side of sports seemed to be at hand. A victory over the army of cheats who seek an unfair advantage by injecting blood booster EPO and testosterone or by taking anabolic steroids.

"Hilton Hotel Security found another syringe in the room of two athletes." That's how Victor Burgos, an investigator for the U.S. Anti-Doping Agency (USADA), began an email he sent on Nov. 22, 2015, at 5:24 p.m. A former policeman from New York, Burgos wrote: "I passed the information, athlete names and room number to Brad and he is picking up the evidence and handling test planning."

USADA headquarters is located in an office complex in the town of Colorado Springs at the edge of the Rocky Mountains. The men and women who work here are considered the most tenacious doping investigators in the world. In recent years, the agency has uncovered the doping practices of some of the biggest names in sports, including cyclist Lance Armstrong and the world-class sprinters Tyson Gay and Marion Jones.

The message sent by Burgos electrified the headquarters staff and USADA head Travis Tygart wanted to know where the athletes were from. Bradley Guye, who took the lead on the case, replied that they were two female weightlifters from Egypt. The pair was staying at a Hilton Hotel in Houston, where the world championships were taking place.

Guye inquired as to whether he should perform a drug test. "Yes," answered USADA headquarters, adding that, in addition to urine, blood samples were also necessary to determine by way of a DNA test which of the athletes had used the syringe that had been found.

In a message a short time later, Guye reported that there were anonymous eyewitnesses claiming to have seen a male weightlifter injecting himself with something before weighing in prior to competition.

There was quite a bit going on, it seemed, at the world championships in Houston. USADA head Tygart was stunned. "Wow … this is the Wild Wild West!" he wrote in an email.

The names of the two weightlifters, in whose room the syringe was found, are unimportant. They only made a brief appearance on the investigators' radar before disappearing again. They were tested in their Houston hotel room, but the results were negative. The investigation had been in vain.

In a report to the global weightlifting federation, USADA wrote that it might make sense for the organization to introduce a "no-needles policy" for the sport. But they couldn't do much else.

The fight against doping is comparable to the battle against drugs: There is no real way to win it. But it must be fought nonetheless. Otherwise, all control would be lost.

Dopers have become increasingly unconscionable. They continually find new methods and they can count on an army of accomplices to aid them in their fraud: dealers, doctors, trainers and officials who supply their clients with the necessary substances -- and charge a fair amount for doing so.

Most countries that send athletes to the Olympic Games have special institutions that are responsible for going after the dopers. These national anti-doping agencies are akin to small outposts on a vast front line. Some of them take their jobs seriously, but not all.

USADA is among the most effective organizations in the fight against doping. It employs medical professionals, chemists and forensic experts who are intimately familiar with the lists of banned substances and the active ingredients they contain in addition to the doping practices used by athletes. The agency's 100 or so employees send out investigators to check on athletes who have fallen under suspicion.

Until now, little had been known about how the agency goes about hunting down suspected dopers. But in December, the hacker group Fancy Bears provided SPIEGEL with several sets of data containing PDF and Word documents in addition to hundreds of internal emails from USADA and WADA, the World Anti-Doping Agency. The material provides a look at the day-to-day work of the agencies during the Olympics year of 2016: how they did their research, the tactics they used and the actions they took if they suspected a violation.

The data also reveals the frustration they experienced when investigators were on the heels of a doping cheat, but were unable to bring him or her to justice -- and their frustration that such failures lead to ongoing sordidness in the sporting world.

Ozone Therapy

WADA is the umbrella organization of all doping investigators. Each year, it publishes a list of banned substances and treatments and currently, there are around 300 substances on the index. More are added all the time. A drug that may have still been allowed at the beginning of the year could result in a doping ban just a couple of months later.

It is up to the athletes to keep track of what is allowed and what is not, but for many of them, doing so is apparently a significant challenge. USADA staff is frequently surprised by how little some athletes know of the rules -- or want to know.

In early May, three months before the opening ceremony in Rio, the phone rang at the information hotline run by USADA. An athlete was on the other end of the line and mentioned during the conversation that he had used ozone therapy. The USADA employee was shocked.

Ozone therapy involves withdrawing blood, enriching it with an ozone-oxygen mixture and then reintroducing it into the veins. The method is considered a form of blood doping and has been banned by WADA since 2011. The athlete on the phone, though, claimed he had "no idea."

The athlete's doctor, who then contacted USADA, likewise professed to being "completely surprised" that blood treatment was not allowed for athletes. Fully five years ago, 30 German athletes had been under suspicion of doping because they had had their blood treated by a medical professional.

A USADA agent wrote a friendly letter to the American Association of Ozonotherapy. "We have unfortunately witnessed situations where health care providers have unwittingly jeopardized athlete eligibility as a result of unfamiliarity with the fact that that IV infusions, the delivery of blood products and other therapies involving the blood, such as ozone therapy, are 'prohibited methods' according to the World Anti-Doping Agency. … Health care providers in your organization may be unaware (of) that."

The letter also included the terse observation that doctors who perform unauthorized procedures on athletes are punishable by law.

Fish Oil and Cortisone

Doping investigators are well aware of just how corrupt the top levels of sports are. But part of their job is helping athletes and informing them of what is allowed and what is not. Often, athletes contact the agency to ask about whether certain cough medicines can be taken without fear of reprisal. On one occasion, a world-class triathlete sent an email because she wanted to know the blood values from a doping test that she had undergone. She was politely informed that USADA does not provide such data for fear that it might be used for "self-diagnosis" or self-treatment. Have a nice day.

A what point, though, does doping actually begin? As part of each doping test, athletes have to fill out a "Declaration of Use" (DOU) form in which they must indicate which medicines and other substances they have taken in the past seven days.

SPIEGEL is in possession of the DOU forms submitted by dozens of American athletes, including cyclists, soccer players and track-and-field athletes. They show that in the run up to Rio, athletes took pretty much everything that was available on the legal market.

There are weightlifters who take milk protein to build up their muscles, tennis players who use acylcarnitine to improve their concentration and triathletes who swear by fish oil, for no discernible reason.

Some DOUs are rather questionable. Galen Rupp, who won the marathon bronze in Rio and who is considered the fastest white long-distance runner in the world, takes the asthma medicine Advair. He also takes Combivent, a medicine that expands the airways, and Cytomel for weight loss.

On his form, Rupp wrote that he takes the medications merely to treat conditions such as asthma and an underactive thyroid gland. "None of the medicines … are banned."

That is true. Most of the substances listed by athletes in their DOUs are allowed. But it is nevertheless a gray area because the consumption of such medications has become so excessive. Most athletes seem to follow the strategy of taking as much as possible. They swallow all manner of substances in the hope of seeing some sort of benefit.

Like Justin Gatlin. The 100-meter Olympic gold medalist in 2004 apparently eats dietary supplements like they are candy. In his DOU from spring 2016, he listed all of the products that he had consumed:

Beta-alanine, amino acid, one spoonful;
Calcium and magnesium, one spoonful;
EPIQ 3X Muscle, a muscle-growth supplement, one tablet;
EPIQ HEAT GC, a weight-loss supplement, one tablet;
EPIQ Ripped, another weight-loss supplement, one tablet;
EPIQ Protein, a regenerative supplement, one spoonful;
EPIQ Test, a testosterone booster, one tablet;
MD Plus Test, another testosterone booster, one tablet;
MD Plus G Boost, a muscle-growth preparation, one tablet;
MD Plus Lipoflush, a substance to promote the burning of fat, one tablet;
MD Plus Power Drink, one spoonful;
MD Plus Thermo Cell, another weight-loss supplement, one tablet.

All of the above preparations can be ordered with just a few clicks on the internet. Gatlin reported that he took all of the substances on April 18 -- eight tablets and four powders, all in just one day.

The transition from such legal performance enhancement to actual doping is sometimes rather fluid. World-class athletes spend a significant amount of time searching for new preparations and methods that aren't yet on the list of banned substances and practices -- anything that promises some sort of positive effect.

The Fancy Bears documents show that U.S. sprinters Allyson Felix and Sanya Richard-Ross, both of whom have won multiple Olympic gold medals, have taken dexamethasone, known as dex for short. It is a cortisone preparation that helps mountain climbers combat the effects of altitude sickness, improves concentration and accelerates recovery.

Battling the Unknown

Dex appears to be quite popular among American track-and-field athletes. On July 2, one month before the Rio games began, a well-respected doctor contacted USADA. He was providing medical care to the Olympics team and had previously worked for an NBA basketball team. In an email, he asked if treating athletes with dexamethasone by way of iontophoresis was banned. Iontophoresis is a procedure through which medication is introduced into the body by way of electrical current, applied using electrodes taped to the skin.

The USADA staff was puzzled. Iontophoresis? They didn't have any experience with the method at the time. Sometimes, things are complicated, leading to moments when even the experts aren't totally sure what constitutes doping and what does not.

Ultimately, USADA Science Director Matthew Fedoruk addressed the issue. He responded: "Dexamethasone is prohibited in (competition) by oral, IM, IV and rectal routes. Topical or Iontophoresis routes (...) are not prohibited. Cheers, Matt."

It was good news for the track-and-field athletes' doctor. He had found a new, legal method for administering a substance that was essentially banned -- even during competition.

Syringes in the Locker Room

USADA has existed for 17 years. Most of its funding comes from the state, with the U.S. government pumping around $9 million per year into the fight against doping. The U.S. National Olympic Committee supplies another $4 million annually.

Last year, USADA carried out over 10,000 doping tests. Swimming star Michael Phelps was tested 13 times, four-time Rio gold medalist swimmer Katie Ledecky submitted to 19 tests, Justin Gatlin was checked 14 times and Allyson Felix 12. Among the American star athletes, not a single test was positive.

In 2016, USADA issued sanctions against 60 athletes, including athletes in the martial arts, second- and third-tier cyclists, weightlifters, one roller hockey player and an equestrian athlete, among many others. The doping investigators take every suspicion seriously and look into every abnormality, even if the athlete involved is far from the top of his or her sport.

At the end of March, for example, the inspectors discussed a sample belonging to a 55-year-old senior track-and-field athlete. They had found traces of metabolites in the woman's urine that indicated the possible use of metandienone. The anabolic steroid has been favored by athletes for decades and is sometimes referred to by its nickname "breakfast of champions." The case was referred to a USADA scientist, but he was unable to isolate sufficient metabolites characteristic of the steroid to warrant the opening of an official investigation. "More nails in the coffin" were needed, he wrote, and the case was shelved.

For doping inspectors, it is important to expose big-name athletes every now and then. An elaborate testing system can only be justified if it is able to identify cheaters at the highest levels of sports. Germany's anti-doping agency, for example, hasn't managed to catch anybody of note in recent years and has gained a reputation for being little more than a urine sample collection agency that provides the German sports world with a clean conscience.

USADA, by contrast, owes its elite reputation primarily to its victory over Lance Armstrong. The battle against the former cycling professional was long and drawn-out, but in 2012, he was banned from cycling for life and lost his seven Tour de France championships.

Investigators with USADA don't exclusively rely on doping tests. The emails seen by SPIEGEL indicate that the agency also works closely with insiders and anonymous informants.

One of these whistleblowers got in touch on July 13, three weeks before the opening ceremonies in Rio. USADA received an email with the subject line: "Inquiry." Importance: "High."

The message included the report of an employee of USA Swimming, the country's swimming association. The man detailed an incident that was believed to have occurred at Lynbrook High School in San Jose, California during a Chinese Olympic team training camp. In July 2016, top Chinese swimmers were preparing in the U.S. for the Rio Games.

The informant wrote that the father of an athlete with the local swimming club witnessed on July 7 at Lynbrook High School "members of the Chinese national team injecting themselves with needles in the locker room. They were also ingesting pills. When asked by the parent (who speaks Mandarin) about what they were doing, the athletes said it was nutrients and vitamins."

The information triggered a lively email exchange. Molly Tomlonovic, coordinator for the doping tests, issued assignments to her team of investigators not unlike a police chief at the station. She requested that doping control officers be sent out and asked for information regarding their training times at the pool and where they were staying while in California.

With assistance from WADA, Tomlonovic was sent a list containing the names of the Chinese swimmers, many of whom had won medals at previous world championships and past Olympics. The athletes had only seldom or never been tested for human growth hormone or EPO, an additional item of information states, noting that the required blood tests are seldom undertaken in China.

The emails viewed by DER SPIEGEL do not indicate how the case involving the Chinese athletes proceeded. In response to our queries, USADA officials said that on July 16 and 17, the agency conducted urine tests on 22 Chinese swimmers. USADA did not say whether any of the tests had come back positive. The investigators planned to conduct a second set of tests five days later, but the Chinese had already left.

The Chinese Swimming Association denies that any doping took place at the U.S. training camp. "Anyone with basic common sense shall understand these information (sic) are ignorant and outrageous, and malevolent," an official stated. The official said there was a "zero tolerance" approach to doping.

We do, however, know that Chinese swimmer Chen Xinyi tested positive at the Rio Olympic Games for hydrochlorothiazide, a diuretic that can be used to mask doping substances. She has been banned from the sport for two years.

Blood Doping and Cocaine

Years in which the Olympic Games take place are always peak periods for doping. In order to win medals, many athletes swallow and inject whatever they can get away with. The investigators, too, are constantly at work. Their aim is to catch as many cheats as possible before the start of major sporting events.

It's always a race against time because - and this is the sad reality in the battle against doping - the investigators seldom win.

On July 14, WADA requested administrative assistance from USADA. Stuart Kemp, WADA's deputy director, wrote that nine international athletes would be preparing for Rio in the United States and that they were a "high priority" for investigators. So far, he wrote, "no tests have been accepted."