William F. Sweeney Jr., head of the F.B.I.’s New York office, added, “What actually happened to the horses amounted to nothing less than abuse.”

Horse racing has a long history of trainers’ repurposing drugs in pursuit of a performance edge. Frog and cobra venom, Viagra, cocaine, heart medicines and steroids have all been detected in drug tests. This reliance on performance-enhancing drugs combined with lax state regulations has made American racetracks among the deadliest in the world.

Nearly 10 horses a week on average died at U.S. racetracks in 2018, according to the Jockey Club’s Equine Injury Database. That figure is anywhere from two and a half to five times greater than the fatality rate in Europe and Asia, where rules against performance-enhancing drugs are enforced more stringently.

Servis and Jorge Navarro, whose horses have earned more than $37 million since 2008, were the most prominent trainers named in the indictment. Both are based in the Mid-Atlantic and at times conspired to keep their cheating from being detected, according to the indictment.

On Feb. 18, 2019, Servis alerted Navarro via text message that a racing official was in the barn area near where they kept the prohibited joint blockers and blood builders that they referred to as “red acid” and “monkey,” the indictment said. On the same day, Navarro was overheard on a call with another defendant, saying that he would otherwise have been caught “pumping and pumping and fuming” every horse that ran that day.

Servis and Maximum Security, who has won eight of his 10 starts and nearly $12 million in purses, have become favorites of horse racing enthusiasts largely because of what many thought was an unjust disqualification in America’s most famous race. The indictment says Maximum Security was given performance-enhancing drugs.

On June 5, 2019, Maximum Security was drug-tested at his Monmouth Park barn on the Jersey Shore as Servis was preparing him to run in the Pegasus Stakes. In a phone call intercepted by the authorities with one of his veterinarians, Kristian Rhein, Servis indicated that Maximum Security had received a shot of SGF-1000, a compounded drug aimed to enhance performance, the indictment said.