OTTAWA - Former Mountie Kevin Gregson told his father he was a "monster" after he was confronted with allegations he'd raped a 10-year-old, hours before he killed an Ottawa Police officer, Gregson's sex assault trial heard Tuesday.

"He said he'd done something pretty stupid and if he was convicted it would probably be 10 years," Reid Gregson testified his son said late on Dec. 28, 2009, after arriving at his father's home unannounced.

"As he stood at the door he said, ‘I'm a bad guy, I'm just a monster and I've done very bad things,'" said the elder Gregson, who believed Kevin was talking about things he'd done as a police officer.

Kevin Gregson, 46, said he'd failed to kill himself earlier but was going to find a better way to do it, court heard. Early the next morning, he stabbed Constable Eric Czapnik to death.

The murder trial heard that Gregson -- his RCMP career over -- carjacked a vehicle, put on two bullet-proof vests, armed himself with a pair of knives and went to the Civic campus of the Ottawa Hospital.

He ambushed Czapnik, 51, as he sat working in his cruiser outside the emergency room and tried to wrest away his gun.

Convicted in March of first-degree murder, Gregson has pleaded not guilty to charges he sexually assaulted a little girl four times in the week before the murder.

His ex-wife testified Tuesday that he denied the rape allegations when she confronted him but told her he's "done" and "can't recover from this."

"He said it will be the last time we see each other like this," the woman said at Gregson's trial on sex charges. "He said the RCMP is going to jump on this regardless of whether it was the truth or not. I asked him twice if he did what she said. He denied it."

In a heart-breaking video shown in court, the girl told police in horrific detail that Gregson raped her twice on two separate days.

The girl's blood and a mix of her and Gregson's DNA were found on a mattress, Det. Todd Campbell testified. The stain with Gregson's DNA wasn't blood but couldn't be conclusively identified.

The trial continues Wednesday with testimony from two doctors about the injuries she suffered.