OAKLAND -- An Oakland police DNA expert admitted Wednesday that she made a mistake in collecting a blood sample from a pillar inside the entrance to murder defendant Hans Reiser's home.

Under cross-examination by Richard Tamor, one of two attorneys representing Reiser in his trial on charges that he murdered his estranged wife Nina, criminalist Shannon Cavness said she only collected one blood sample from the pillar but she should have collected at least two samples and could have collected as many as five samples.

Cavness said that if she were to examine evidence at Reiser's home at 6979 Exeter Drive in the Oakland hills again, "I would have swabbed at least two distinct areas."

She said, "I was assuming they (the blood stains) were from the same source, which was a mistake," because the stains were from at least two different sources.

Hans Reiser, a 44-year-old computer engineer, and Nina Reiser, who was 31 when she disappeared Sept. 3, 2006, after she dropped off the couple's two children at his home, married in 1999 but she filed for divorce and separated from him in 2004. The couple was in the midst of an acrimonious divorce and a battle over the custody of their children when she disappeared.

Her body has never been found, despite extensive searches in the Oakland hills and elsewhere.

Hans Reiser has pleaded not guilty to the charges against him.

Under questioning from prosecutor Paul Hora on Tuesday, Cavness said blood that very likely came from Nina Reiser was found on the pillar inside Hans Reiser's home as well as on a sleeping bag sack that was found in his car when it was recovered several weeks after Nina disappeared.

Cavness, who was deemed to be an expert witness by Alameda County Superior Court Judge Larry Goodman, said there is a less than 1 in 45 trillion chance that the female blood samples on those two locations were from someone other than Nina Reiser.

Cavness also said there is a less than 1 in 208 chance that a male blood sample on the pillar came from someone other than Hans Reiser.

She said the reason for the large difference in odds is that the female sample was much bigger than the male sample, which was nearby.

In addition, Cavness said there's a less than 1 in 1 billion chance that a male blood sample found on the sleeping bag sack was from someone other than Reiser.