Calgary paramedics tend to RCMP Sgt. Andrew Johnson after he was stabbed Tuesday. (Courtesy of Calgary Sun)

A veteran Mountie is expected to recover from serious stab wounds after he and a fellow investigator were attacked in the Calgary office of the Alberta Serious Incident Response Team on Tuesday.

The late-morning stabbing occurred at the J.J. Bowlen Building, a former courthouse on Seventh Avenue S.W. that now houses ASIRT, the provincial agency that investigates serious cases of death or injury involving police officers.

Sgt. Andrew Johnson, a plainclothes RCMP officer assigned to ASIRT, had escorted a man who showed up without an appointment into an interview room, said Clifton Purvis, head of ASIRT.

CBC News confirmed the man, Lee Christopher Monrose, 30, was shot in the head by police during a confrontation in November 2009. ASIRT is investigating Monrose's shooting.

Purvis told reporters that while at the ASIRT office on Tuesday, Monrose became more and more agitated.

A suspect is taken out of the J. J. Bowlen building in Calgary after two police officers were attacked by a man with a knife. (Courtesy of Calgary Sun)

"Over about 10 minutes, it appears that his behaviour escalated," Purvis said. "He became violent, and he attacked one of our investigators in the office."

Two other ASIRT investigators — one from the RCMP and the other from the Calgary police — rushed into the room to help Johnson, 53.

While scuffling with the man, the Calgary police officer suffered a knife wound to his hand. He was treated at the scene.

The Mountie, who was stabbed three times in the upper torso, was taken to the Foothills Hospital in serious, life-threatening condition. He underwent surgery and is scheduled for a second operation.

"He has been updated to serious but stable condition, but to be clear, his injuries are very, very serious," said Stuart Brideaux, a spokesman for Calgary EMS.

Johnson, a 25-year veteran of the RCMP, has been working with ASIRT for the past two years. His wife and two sons are with him at the hospital, Purvis said.

Monrose was transported to hospital but only suffered a bump on his head, officials told CBC News.

Attacker shot by Calgary police last year

Monrose's November shooting occurred after two Calgary police officers in a cruiser approached a seemingly suspicious SUV in a northeast park. Monrose was shot when he reportedly tried to ram the cruiser with his vehicle.

No charges were laid against Monrose in connection with the shooting, but he is facing charges stemming from another incident in summer 2009, including assault with a weapon, mischief causing property damage, failing to stop for police and Traffic Safety Act violations.

Sgt. Andrew Johnson is in hospital with serious stab wounds. (RCMP)

ASIRT coincidentally started a security and risk assessment review two weeks ago, said Purvis.

Anyone arriving at ASIRT's Calgary office has to be buzzed in, but there are no metal detectors and there's no policy to search people who enter. Purvis said the suspect was allowed into the secure area because he was known to investigators.

"At the time [the suspect] was brought into the secure perimeter, there was nothing to indicate that his intentions were violent," said Purvis.

ASIRT officers have access to body armour and weapons, but it's up to them to choose when to wear them. Johnson was not wearing any protective gear when he was stabbed.

In a formal interview, ASIRT staff would be recording the conversation on audio and video. "Because of the relative innocuous nature of this exchange, it wasn't considered a formal interview so those practices weren't followed," said Purvis.

Edmonton police to investigate

Calgary police Duty Insp. Vic Trickett said the municipal police force generally does not have a reason to pat down a witness before an interview.

Edmonton police have been asked to take over the investigation because so many agencies are involved, including ASIRT, the RCMP and the Calgary Police Service, explained Trickett.

"At all times, we have to ensure there's impartiality within the investigation itself, and that's the best way to do it," he said.

ASIRT is led by Purvis, a lawyer and Crown prosecutor, and includes other civilian analysts and investigators, as well as 10 police officers.

With files from the CBC's Mary-Catherine McIntosh