Roger Clemens will have a hard time explaining this one.

Alan Keel, a forensic scientist, testified Friday in Clemens' perjury trial that two cotton balls and a syringe needle allegedly kept after a steroids injection matched the former pitcher's DNA.

Keel explained in court that the cotton balls had DNA that was "unique to one person who has ever lived on the planet." The syringe was less conclusive because there were only a handful of cells present.

The medical waste was saved by Brian McNamee, Clemens' former strength coach, after he allegedly injected Clemens with steroids in 2001.

Clemens is on trial for perjury, accused of lying about his denial of steroid use during a 2008 congressional deposition. McNamee is the prosecution's key witness.

The new finding deals another blow to Clemens' case. His lawyers did not try to deny the presence of his DNA or steroids on the material. Instead, they claimed that McNamee applied the steroids to the needle after injecting Clemens with a vitamin B12 shot.

This defense was quickly refuted by Keel, who claimed there was no way to fake this.

"If this were contrived, I would expect to obtain much more biological material," he said, explaining that it would be difficult to forge a sample with such a small amount of biological material on it.

Keel also eliminated the possibility of contamination by stating that if there was contamination, McNamee's DNA would have been found on the needle, which it was not.