Paramedic eyewitnesses began to take the stand in the trial against a former Mountie accused of killing Ottawa police officer Eric Czapnik two years ago.

Craig MacInnes was the first of three paramedics to recount the early morning of Dec. 29, 2009, which is when Czapnik was fatally stabbed outside the Civic Campus of the Ottawa Hospital.

Kevin Gregson is charged with first-degree murder in the death.

MacInnes told the court Wednesday he saw a silver car pull up near the ambulance area of the hospital around 4 a.m. on Dec. 29 and then a man stepped out of the car with "something brown" in his hand.

Within a minute, the paramedic said he ran outside and saw both Czapnik and Gregson on the ground struggling. Gregson, he said, was on top of Czapnik punching. MacInnes estimated Gregson used a short, repeated stabbing motion six-to-eight times while straddling both sides of Czapnik's chest.

MacInnes then said he decided to put his arm around Gregson's neck, twisted and pulled. When he looked at Czapnik, there were "copious amounts of blood" coming from his neck.

Paramedic gives emotional testimony

Paramedic Patricia St. Denis also had a tear-filled testimony Wednesday afternoon. She told the court she saw Gregson wrestling with MacInnes.

Const. Eric Czapnik died after he was stabbed in the neck on Dec. 29, 2009. (Ottawa Police Service)

She then said she wanted to help him but saw a knife in Gregson's hand and yelled "he has a knife".

As the paramedics fought off Gregson, MacInnes added Czapnik stood up and could not speak so he told him to go inside the hospital's emergency room. St. Denis also said Czapnik mouthed the words "thank you".

The paramedics also said Gregson was emotionless when he was handcuffed and apprehended. Both MacInnes and St. Denis said Gregson told them, "I just needed a gun. If he'd just given me the gun."

Bloody murder weapon presented to jury

Also on Wednesday, the jury was handed a blood-stained, double-edged knife believed to be the same one used to stab Czapnik. MacInnes identified the knife as the one Gregson was holding when MacInnes confronted him.

Ottawa police Det. Ugo Garneau also showed the judge and 12 jury members photos of Gregson after his arrest, which showed cuts to his neck and hands and abrasions on his face and knees.

The jury also examined Gregson's two vests of body armour, which showed no cuts or damage, as well as Czapnik's kevlar vest, which had knife cuts and was covered in dried blood.

Assistant Crown Attorney Meaghan Cunningham told the court Tuesday Gregson had confessed to police in a videotaped interview he had killed Czapnik in order to get the constable's gun.

The court also heard Gregson was wearing two bullet-proof vests and carrying two knives, a gun and handcuffs after he was arrested on the night Czapnik died.

Gregson pleads not guilty to murder, robbery

Gregson has pleaded not guilty to first-degree murder in the death of Czapnik, 51, a father of four who had joined Ottawa police two years earlier as the oldest ever recruit in the force's history.

Gregson also pleaded not guilty to robbery in relation to a carjacking the night before the stabbing.

Crown prosecutors aim to prove the charges through Gregson's knowledge Czapnik was an on-duty police officer, not pre-meditation.

Both sides agreed on a number of facts Tuesday, including that Gregson stabbed Czapnik, Gregson knew Czapnik was a serving police officer, photo evidence submitted in the trial is genuine and an RCMP witness can testify to Gregson's RCMP record even if not personally involved.

Two police officers presented evidence Tuesday, including Const. Richard Lechleitner, who identified Gregson as the man he saw in the back of the police cruiser after Czapnik had been stabbed.

Defence counsel is expected to lay out their case after the Crown has finished presenting its evidence.