WASHINGTON — Brian McNamee’s estranged wife gave a different account today from her husband’s about how he started collecting alleged medical waste from injecting Roger Clemens with performance-enhancing drugs.

McNamee, Clemens’ former strength coach, testified last month that because of his wife’s nagging, he brought medical waste from a steroids injection of Clemens home in 2001. He said he showed it to her, and she said, “all right,” and he said he stored it in a FedEx box.

But Eileen McNamee testified today that when she first saw the FedEx box and asked him about it, her husband said it wasn’t of her concern. She said that McNamee said he was saving things for his “protection.”

That motive, however, is consistent with McNamee’s testimony that the goal, prompted by his wife’s nagging, was to have evidence to prevent McNamee from becoming the sole fall guy if the purported drug abuse became known.

Clemens’ lawyers hope Eileen McNamee, who has been given immunity to testify, will help discredit her husband, the government’s chief witness.

Earlier, a defense expert testified that DNA from Clemens found on a syringe needle could have been placed there intentionally.

Mark Scott Taylor, a DNA expert and president of Technical Associates Inc., also said he couldn’t rule out that Brian McNamee’s DNA was on the needle. McNamee has said he saved the item and other medical waste after injecting Clemens with steroids.

Taylor’s testimony was part of a two-day attack by Clemens’ lawyers on the physical evidence against the former pitcher, who is charged with lying to Congress in 2008 when he denied using steroids or human growth hormone. The defense has been trying to show multiple reasons or theories that the physical evidence might not necessarily support McNamee’s testimony that he injected Clemens.

The government’s DNA witness, forensic scientist Alan Keel, testified last month that it would have been impossible to fake the evidence on the needle because the amount of biological material on it was too small.

Taylor disagreed with that.

“We’re dealing with a situation — how much DNA (was there) won’t be readily understood by someone who doesn’t have expertise in this area,” he said.

Taylor’s testimony was interrupted after the government objected to a question from Clemens lawyer Michael Attanasio about the possibility of steroids being added to two cotton balls after the pitcher’s biological material was on them.

With the jury cleared, prosecutor Courtney Saleski complained that Taylor was providing a new opinion.

“I would have liked to be prepared for this,” she said.

U.S. District Judge Reggie Walton agreed.

“It should have been provided” to prosecutors, he said. “There’s no excuse for this, Mr. Attanasio.”

“You all have been playing fast and loose, and I’m sick and tired of it!” he yelled. Walton said he blamed both sides, and noted that if he keeps Taylor off the stand, that would be unfair to Clemens. “Sometimes when you roll the dice, you lose!”

After a break, Saleski said she was prepared to cross-examine Taylor, and his testimony continued.

Clemens’ defense may have regained the momentum the day before when a scientist testified that the government’s physical evidence against Clemens could have been contaminated.