When last seen, Charles Sly starred in a do-it-yourself YouTube confession in which he insisted that everything he had said to an undercover Al-Jazeera reporter about banned substances and professional athletes, including Peyton Manning and Ryan Howard, was a fabulous lie.

“To be clear,” Sly said, “I am recanting any such statements and there is no truth to any statement of mine.”

Manning denounced Sly as a liar, as did the quarterback’s spokesman, Ari Fleischer, who accused Al-Jazeera of deeply irresponsible journalism.

“Al-Jazeera is backtracking and retreating,” said Fleischer, the former White House press secretary for President George W. Bush.

Maybe they are right. Maybe Sly is a truth-challenged, unmade bed of a man who spins slanderous tales. Or maybe, as Sly claimed, he intentionally fed misleading information to Al-Jazeera’s undercover reporter.

I listened, and I read the transcripts of the Al-Jazeera video recordings as Sly spoke with great detail and expertise of doping and tossed out several athletes’ names: baseball players Howard and Ryan Zimmerman and football players Manning, Mike Neal and Dustin Keller.

As I turned over the possibility that Sly had lied to the undercover reporter, I kept coming back to the names. Why these specific athletes?

With the help of my New York Times colleagues Ken Belson and Doris Burke, I scrutinized the list of names, and it soon appeared less random than at first blush. Nearly all the athletes he named are clients of Jason Riley, a fitness trainer based in Sarasota, Fla.

Here is where the story of Charles Sly becomes more intriguing.

Sly is a business partner of Riley’s. When Sly applied for a pharmacist license in Florida, he used Riley’s home address.

Riley and Sly founded Elementz Nutrition, a nutritional supplements company whose website and Facebook page feature many athletes Sly mentioned on camera. Zimmerman is featured on the website; Howard, Neal and Keller on the Facebook page. In one photograph on Facebook, Riley poses at his gym, the Compound, between the mountainous Howard and the no less imposing Neal.

Not every athlete cited by Sly in the Al-Jazeera report is connected to Elementz, and not all of Elementz’s big-time clients were mentioned by Sly.

Elementz proclaims all-natural bona fides. According to its website, it specializes in “vitamins, minerals, proteins and enzymes [that] are essential for our bodies to perform.” In other words, chia seeds, flax, whey and all that.

Riley’s work as a trainer is so celebrated that he carries a reputation as “baseball’s MVP of the post-steroids era.”

His most famous client, the man whose career he was credited with reshaping and saving from mortality’s shadow, was Derek Jeter. In 2010, a few years into Riley’s makeover, The Daily News proclaimed: “Derek is turning back the clock at short.” ESPN declared Riley “dumped the Captain into a hot tub time machine” and turned him into a 25-year-old.

Significant caveats are in order here: No evidence has emerged linking Jeter to performance-enhancing drugs, and Sly did not connect him to banned substances, although he boasted of helping other athletes obtain them. And a connection to Sly, Riley or anyone else is hardly proof of any wrongdoing.

Sly and Riley did not respond to several interview requests. An email sent to Elementz’s angel investor, Janis Krums, went unanswered. Jeter’s agent, Casey Close, did not respond.

Mum’s the word on the west coast of Florida.

Howard and Zimmerman let their lawyer, William Burck, address the Al-Jazeera documentary: He called it reckless, wholly false and unsubstantiated.

We will, Burck promised, go to court.

Manning, too, has rumbled about filing a lawsuit. As of now, no one has filed court papers. Zimmerman’s photo, however, disappeared from the Elementz website last week.

As for Neal, the Green Bay Packers linebacker, Sly described him as a close friend. Neal went to Merrillville High School in Indiana, about a 90-minute drive from where Sly went to high school. In the documentary, Sly said that he spent about six weeks in Green Bay and that Neal, who served a four-game suspension for doping in 2012, introduced him to about half the team.

None of this amused Neal.

“I’m sure you saw how pissed off Peyton Manning was about somebody coming out with false accusations,” he told reporters last week. “So if you want to piss me off, that’s one thing. But please don’t.”

The Elementz Facebook site features several photos of Neal: “Mike Neal dedicated to Nutrition programs to maximize his career longevity.”

It’s difficult to get worked up over the possible doping of football players. NFL players are the closest approximation we have to gladiators, and some ingest or shoot up whatever is needed to get them through another bloody and bruised Sunday, Monday or Thursday. Pain, and the specter of brain trauma, will be their lifelong companions.

But what to make of Sly? In the end, this story hinges on his credibility. A man who operates in the athletic shadows, he was confronted with his hours of undercover interviews, and recanted. He proclaimed himself an idle boaster.

What was he supposed to do, if what he had said was true? Acknowledge it and allow his words to become his manacles?

Mitosomal growth factors, stem cells and pig brain peptide: He talked of all with a chemist’s ease. His network, as he described it, extends from Germany and Switzerland to Vancouver, where Chad Robertson, a pharmacist, said Sly was a savant of doping.

The Al-Jazeera documentary was only the latest report to reveal sports doping as a spider’s web that stretches across continents and oceans. You wonder if the pro league chieftains, Rob Manfred in baseball and the NFL sachem Roger Goodell, have paid attention, and have the stomach to pursue these strands.

They might want to hurry. Last week, Elementz Nutrition voluntarily dissolved and closed its doors.