Kevin Gregson said he "killed" Const. Eric Czapnik, but didn't "murder" him as he began to testify in his own defence Thursday.

"Eric Czapnik, the man I killed," said the man accused of first-degree murder in the police officer's death. "I killed him, but I didn't murder him."

The former Saskatchewan RCMP officer is accused of stabbing Const. Eric Czapnik to death in the parking lot of the Ottawa Hospital's Civic campus on Dec. 29, 2009.

Gregson said he doesn't remember parts of that night after a failed suicide attempt, but said he went to the hospital because if no police were there he would check himself into the mental ward.

Instead, he said found Czapnik doing paperwork in his car. He said he pointed a BB gun at him and told the officer to get out.

After a short struggle Gregson said he used his weapon.

"My knife went up - boom, boom. I stabbed him," he said. "I didn't do it intentionally. I just did it. There was no intent . . . It's all training, I just reacted."

"That's why I'm pleading not guilty; this should be a manslaughter charge."

His self-admittedly rambling testimony included many stories from his early police days, claims a co-workers wanted to swap wives with him and an admission he slept with his mother's hairdresser.

"To you guys I'm a potential monster, to my mom I'm five; I'll always be five," he said as he became emotional.

As his testimony finished for the day, he said Czapnik was a good man and he was sorry for killing him.

"I didn't go there to kill a cop," he said. "I was going to use force and cuff him and I almost did until he went for his gun."

It's expected Gregson's lawyers will use cysts found on Gregson's brain as a big part of their defence.

"In 2006 I thought I had strep throat, so I went to the hospital and I passed out," said Gregson. "Then they found out I had things on my head," that he said were colloid cysts.

Crown finished its case on Wednesday

Gregson took the stand at the Ottawa courthouse after the Crown finished calling witnesses on Wednesday.

The Crown had presented interrogation video of Gregson where he said he wanted a gun to kill himself, which Gregson also said Thursday.

This came after his ex-wife said she accused him of sexual assault against a ten-year-old girl.

"My intent was to die," he said in the video. "So I needed a gun. . . police officers have guns . . . so I went to a hospital."

He said during the interrogation and testimony he tried to cut his own throat in the bathtub that night.

Gregson is scheduled to go to trial in September for those separate and unrelated sexual assault charges.

The jury also saw surveillance video from the Ottawa Hospital that showed Czapnik stumbling into the hospital under his own power as he clutched his throat.

The emergency doctor at the hospital that night said they unsuccessfully tried for nearly an hour to stop Czapnik from dying of blood loss.

Later, Gregson is seen on the video being led into the hospital in handcuffs by police.

Court has been adjourned for Thursday, with Gregson scheduled to be cross-examined on Friday.

With a report from CTV Ottawa's Catherine Lathem, who is live-tweeting the trial.