Former Major League Baseball pitcher Roger Clemens walks into the federal courthouse in Washingto last month. (YURI GRIPAS/REUTERS)

A dealer of performance-enhancing drugs livened up the perjury trial of baseball legend Roger Clemens on Tuesday, telling jurors in a thick Bronx accent how he sold the substances to ballplayers and their associates during the height of Major League Baseball’s free-wheeling steroids era.

The testimony of Kirk Radomski, a former New York Mets clubhouse attendant who became a major conduit of steroids to professional athletes, is considered critical to the government’s case because, prosecutors say, he supplied at least some of the drugs used by Clemens.

On the witness stand, Radomski admitted he sold steroids and growth hormones to scores of major league ballplayers for more than a decade until federal agents raided his home in 2005.

In colorful detail, Radomski testified that he sold steroids to Brian McNamee, Clemens’s former strength coach, whom prosecutors say then injected the substances into the pitching star. He and McNamee became friends and discussed the best ways to use steroids, Radomski testified, and the dealer sold McNamee drugs at a diner and in a bank parking lot near the strength coach’s home in Breezy Point, N.Y.

When a prosecutor handed him an evidence bag containing needles, vials and ampules that McNamee later turned over to authorities, Radomski testified that he believed he had sold that very paraphernalia to the strength coach because the products were fairly rare and recognizable.

Often, Radomski said, he tailored his steroids and growth hormones to help pitchers and other players recover quickly and endure a long season. Baseball players, Radomski said, “didn’t want it to be noticeable what they were taking, and pitchers didn’t want to be muscle-bound.”

Shortly after agents raided his Long Island home, Radomski began cooperating with federal authorities and pleaded guilty to money laundering and drug dealing. He was sentenced to five years’ probation in 2008 and faced serious prison time had he not helped the investigation.

Prosecutors displayed pictures of a shipping receipt that Radomski turned over to investigators more than two years after the search of his home. The label is addressed to “B. McNamee” at Clemens’s home in Texas.

Radomski said he found the receipt pinned beneath his television in an envelope that contained signed photos of Clemens and his former teammate Andy Pettitte; Radomski planned to give them to his nephew.

Turning to speak to jurors and knocking on the witness stand to emphasize a point, Radomski spoke so quickly that the court reporter asked him to slow down. Although he used steroids or hormones for years, he described himself as a “health nut” and struggled to spell the names of drugs he took and sold.

“Hey, I’m from the Bronx,” he said. “I’m not a scholar.”

As part of his agreement with the government, Radomski also spoke to former senator George Mitchell and his investigators for a 2007 report about steroid abuse in baseball. The report named dozens of ballplayers, including Clemens, prompting a nationally televised House hearing during which Clemens denied ever taking steroids or HGH. Those denials led to his indictment on charges of perjury, obstruction of Congress and making false statements.

Radomski is expected to be cross-examined Wednesday by Clemens’s defense lawyers. In 15 minutes of such questioning Tuesday afternoon, defense lawyer Michael Attanasio grilled Radomski about being a convicted drug dealer who received a far lighter sentence because he cooperated extensively with authorities.

The trial, now in its fourth week, picked up speed Tuesday after U.S. District Judge Reggie Walton sternly chided prosecutors and defense attorneys for going slowly and warned them that they were boring jurors.

“Those folk are fed up,” Walton told the lawyers, gesturing toward the jury box before the panel of 12 jurors and four alternates entered the courtroom. “You are boring the jurors. Somebody is going to pay a price for that.”