A former Saskatchewan Mountie on trial for murdering an Ottawa police officer in 2009 admitted to killing him but said he didn't "murder" him.

Kevin Gregson, 45, is on trial for the stabbing death of 51-year-old Const. Eric Czapnik on Dec. 29, 2009 in the parking lot of Ottawa Hospital's civic campus.

Gregson made the statement as he testified in his own defence Thursday in an Ottawa courtroom.

"Eric Czapnik, the man I killed," Gregson said in court, "I killed him, but I didn't murder him."

Gregson is also charged with robbery as a result of a carjacking the night before the stabbing. He has pleaded not guilty to both charges.

He said he doesn't remember parts of the night when Czapnik was killed after what he said was a failed suicide attempt on his part. He wanted a gun because he couldn't do it with the knife he had.

He went to the hospital to check himself into a mental ward if no police officer was present, he testified.

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

After a short struggle, Gregson said he stabbed the officer.

"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 rambling testimony included many stories from his early police days, claims a co-worker 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 his lawyers will use cysts found on Gregson's brain as part of the 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

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

"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.

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.