Greg Stejskal didn't need Mark McGwire coming clean Monday about his nearly decade-long steroid usage to know the real story. Stejskal, a retired FBI agent, uncovered the details of McGwire's doping regimen from informants almost two decades ago and, in retrospect, Big Mac is fortunate he wasn't nabbed back then in the federal investigation.

Stejskal, who helped lead the first major federal investigation into illegal steroid distribution called Operation Equine, confirmed that McGwire and his then-Oakland A's teammate, Jose Canseco, were among those identified as steroid users during the probe. The investigation ran from 1989-1993 and led to more than 70 steroid-related convictions, though authorities targeted only suppliers and not users like pumped-up ballplayers.

Federal authorities never considered bringing charges against McGwire, though Stejskal laments that nabbing a big-name athlete might have brought earlier focus to the issue of illegal steroids. That came a decade later with the BALCO scandal and the laundry list of prominent athletes topped by Barry Bonds, Marion Jones and Tim Montgomery.

"With all those 70 some defendants, not one of them was just a user," Stejskal said of the operation. "They were all distributors. Some were distributors and users. We didn't have the resources. We wanted the biggest bang for our buck. We wanted to shut down the black market. We worked the suppliers and there was no reason to go after low-level people."

All these years, Stejskal simply rolled his eyes as Big Mac avoided the steroid question. So he was surprised Monday upon learning of McGuire's admission, which came as he prepares to return to the game as hitting coach with the St. Louis Cardinals.

"I figured that he would either continue to try and finesse the question or back out of the whole coaching thing and say, 'Fine, I'm not going to do this. I don't need this,'" Stejskal said. "It is too bad he waited so long to do it, but I am glad he finally stood up.

"Now I hope he does what he said he was going to do in the [2005] congressional hearings, and that is taking a stand against these performance-enhancing drugs. That he'll fight for more stringent testing and punishment and all that kind of stuff. I don't know that it is going to help him in terms of [election to] the Hall of Fame. I have heard some people speculate that that was part of this, his way of trying to give himself a chance to get into the Hall of Fame.

"But I think everybody suspected that he was doing them. Before, maybe you could have gotten somebody to have given you the benefit of the doubt. Now he is in a situation where you can't even give him the benefit of the doubt. Clearly, he used steroids. And you got to believe they affected his ability."

In a statement made public Monday, McGwire acknowledged using steroids on and off for nearly a decade dating back to 1989. Knowing the questions that await, his admission was careful to specifically cover the 1998 season, when McGwire hit a then-record 70 homers as he and Sammy Sosa engaged in a season-long slugfest that brought a renewal of interest to the sport.

Stejskal said federal authorities, through their undercover operation, learned of McGwire's steroid usage by 1993. A year later, Stejskal recalled that he shared information from the investigation related to baseball players with Major League Baseball's then security boss, Kevin Hallinan, though the sport had no drug testing program at the time.

"We had two sources that told us they personally had seen [McGwire] use steroids," Stejskal told ESPN.com. "Not to mention the fact that Canseco said it as well, which gives you a third source. But we knew it before Canseco said it. And we knew specifics, too. We knew this wasn't a one-time shot or an experimental thing. This guy had a regimen and stuff."

Stejskal has steadfastly refused to identify the sources, though Curtis Wenzlaff has previously been reported to have been a supplier to several Major League Baseball players in the early 1990s, including McGwire. Asked about the sources Monday, Stejskal said, "They were steroid dealers and users who provided information to us that McGwire was a user of steroids." He added that one "was present when he used steroids."

Even so, McGwire stuck to his guns and fended off inquiries about his increasing robust physique and weight gain. He was never more defiant than when he appeared before a congressional hearing in March 2005. Asked whether he took illegal steroids during his playing days, McGwire repeatedly answered "I'm not here to talk about the past."

That performance proved embarrassing and sent McGwire into hiding that past five years. But he isn't about to become subject of a federal perjury probe after his admission Monday.

"He never denied, nor did he admit to the use of steroids," Stejskal said of the Capitol Hill appearance. "He finessed the question. Perjury requires knowingly telling an untruth. He doesn't really say it. He gives that [expletive] comment about, 'This isn't about the past.' Clearly, it was about the past. Now he realizes it was about the past because he clearly put himself in this situation.

"Maybe [Cardinals manager Tony] La Russa or some of these other people said, 'Look, we can finesse this.' So before spring training starts he is out there getting in front of it. That is a good thing. It is just too bad he waited so long.

"He had an opportunity to talk about it in Congress. In a sense, it is vindication for people like the Hootens [whose teenage son Taylor committed suicide while using steroids] who testified just before he did before Congress. Maybe baseball will now realize this was an extremely serious problem and that they are still not in front of it. They are still playing catch-up."

Mike Fish is an investigative reporter for ESPN.com.