The man accused of killing Ottawa police officer Const. Eric Czapnik appeared in court Tuesday after the final person in a 12-member jury had been selected.

The trial began with the Crown's opening statement. The attorney says former RCMP officer, Kevin Gregson, confessed to killing Czapnik hours after the officer was stabbed to death.

Gregson pleaded not guilty to first-degree murder charges on Monday. Now the eight men and four women who make up the jury will help decide his fate.

In her opening statement, assistant Crown attorney Meghan Cunningham describes the night Czapnik lost his life while on duty outside the Ottawa Hospital Civic Campus in December 2009.

She said, after he was stabbed, Czapnik "stumbled 30 feet or so into the emergency room … but couldn't be saved."

Cunningham said hours earlier Gregson was confronted by his wife with serious allegations. The Crown alleges after that he stole a car and drove around looking for a confrontation with police. Gregson is accused of showing up at the hospital "dressed for combat" and armed with "two bullet proof vests, a BB gun and two knives…"

Cunningham said as a former RCMP officer Gregson had special training on how to use a knife and said "that is what he did."

The assistant Crown attorney added that the jury will be able see the video where Gregson is said to have confessed to the crime.

Const. Reinhard Lechleitner was the first witness to take the stand. He had just spoken to Czapnik outside in his cruiser when it happened. He said Czapnik was filling out a report. Lechleitner said he went inside and minutes later was rushed back to the emergency room by hospital staff.

"I noticed the person there was Eric," said Lechleitner. "He was still in uniform and I noticed there was a lot of blood coming from his torso."

Lechleitner went on to say "he was lying motionless."

In court, Lechleitner identified Kevin Gregson as the man paramedics had detained outside in the hospital parking lot.

"Expressionless – I didn't note anger, crying or emotion on his face," said Lechleitner.

Many in the courtroom listened to the dramatic account. Czapnik's wife Anna Korutowska was present.

She has been waiting for proceedings to get underway for two years.

It is not yet known how long the trial will take to conclude.

With a report from CTV Ottawa's Catherine Lathem