Testimony in the trial of a Marion man accused of molesting his girlfriend's then 9-month-old son concluded Thursday with witnesses for the defense challenging the state's version of events.

Prosecutors allege Shane Phillip Nickerson, 21, physically and sexually abused the boy, who is now almost 2 and fully recovered.

But a pediatric sexual abuse expert testified Thursday that while physically abused, the boy's injuries were not consistent with molestation.

"I think he had methadone in his system... he was physically abused," said Lori Frasier, a pediatric sexual abuse expert and medical school professor. "I don't think the evidence is all that strong that he was sexually abused and I think there are other explanations for the findings."

The boy was flown from Kalispell to Sacred Heart Hospital and admitted with extensive bruises on his head, a bloody mouth, and injuries consistent with sodomy and other sexual abuse, according to witnesses for the prosecution.

But the boy's injuries were the product of an open hand slap, rather than being held down and smothered, and insufficient hygienic care, Frasier said.

"There's no real evidence of asphyxiation," said Frasier, who also concluded the boy's respiratory distress came from a source other than fluid in his lungs, most likely methadone.

Frasier also suggested that a portion of a single sperm cell found on the boy's rectal swab may be the result of evidentiary cross-contamination.

The state crime lab proved unable to compare DNA from the cell with DNA taken from Nickerson and two other men.

After discussions with his attorney, Nickerson chose not to testify in his own defense.

Closing arguments are scheduled for this morning, after which jurors will begin deliberations.

Defense attorney Noel Larrivee also sought Thursday to place some responsibility for the boy's injuries with his mother.

Rebecca Taber knew her from before the alleged assault and was at Kalispell Regional Medical Center for unrelated reasons when the boy was brought into the emergency room on Aug. 9, 2008.

"She didn't speak ... she just sat there with her mouth open staring at me," said Taber, who thought the boy's mother was high at the time. "Most of the times I saw her she was high."

Taber testified she notified child protective services after hearing rumors about the woman putting drugs in the boy's bottle.

Nickerson, the boy and the boy's mother all tested positive for methadone, according to testimony.

"I was always concerned about his physical well-being," said Taber, who testified the woman was "absolutely not" a fit mother.

Nickerson pleaded not guilty shortly after his arrest to sexual intercourse without consent, sexual assault, aggravated assault, and one count of criminal endangerment, all felonies.

The Flathead County Attorney's Office added another charge earlier this month, accusing Nickerson of assault on a minor. He has pleaded not guilty to that allegation as well.

If convicted of all charges, Nickerson could be sentenced to more than 200 years in prison and fined $200,000.

Nickerson, who has been in the Flathead County jail since his arrest, also is facing unrelated charges in connection with two alleged altercations involving detention officers.

He has pleaded not guilty to assault on a peace officer and attempted assault on a peace officer and is awaiting trial on those charges.

Reporter Nicholas Ledden can be reached at 758-4441 or by e-mail at nledden@dailyinterlake.com