CTV News has learned more details surrounding allegations that an RCMP officer investigating the Surrey Six slayings had an unprofessional relationship with a witness.

The officer, who is on administrative duties, is a sergeant in the Integrated Homicide Investigation Team and has worked on high-profile homicide cases. He was an investigator in the death of Polish immigrant Robert Dzekanski at Vancouver International Airport.

Meanwhile, the witness is a former girlfriend of several gang members.

RCMP Supt. Janice Armstrong said Wednesday that officials learned of the allegations in December.

She declined to say what the nature of the alleged relationship was, how long it went on for, what role the witness played in the investigation, or how the officer came into contact with her.

On Tuesday, RCMP officials said they had no information to indicate that any criminal investigation had been compromised.

But Armstrong said Wednesday it is difficult to say what the impact will be.

“The information will have to be weighed by Crown Counsel,” she said.

Criminal Justice Branch spokesman Neil MacKenzie said Wednesday that Crown Counsel had not yet received any information from police or evidence from the witness.

Lawyer Terry La Liberte, who is defending one of the Surrey Six suspects, said Wednesday if the allegations are true it could taint the reliability of the witness.

“That witness has to be there presumably to give best evidence possible. This only muddies it up,” he said.

It will also raise questions about other cases the officer has investigated, he said.

“It’s going to concern us with every case he’s ever been involved in.”

Six men, including two innocent bystanders, were gunned down in a high-rise apartment in 2007 in Surrey – the worst gang-related murders in B.C. history.

Six people were subsequently charged in connection with the killings.

One of the six, Dennis Karbovanec, pleaded guilty to three counts of second-degree murder and was sentenced to life in prison.

Five others are awaiting trial.

Eileen Mohan, whose 22-year-old son, Chris, was one of the two innocent bystanders killed, told CTV News Tuesday night that she had been briefed on the internal investigation.

“It’s like we’re seeing a movie here. It only happens in the movies, not in real life. That’s what I thought,” she said.

Mohan said she was initially concerned about how the allegations would impact her son’s case.

But “I was told the case is still very strong,” she said. “This is just one of the hurdles that has come up.”

With a report from CTV British Columbia’s Lisa Rossington