A surveillance book detailing the movement of key suspects in the Surrey Six murder case was left in the former home of an undercover officer for four years before it was returned to the RCMP last month, CBC News has learned from sources.

The 200-page book details RCMP undercover observations, including clandestine photos of suspects gathered during the Surrey Six investigation, a brutal gangland slaying that left six dead in a Surrey, B.C., high-rise.

The book was discovered more than a year ago by RCMP Const. Shane Busch’s ex-wife when she was moving out of their matrimonial home during a bitter divorce.

Busch’s brother-in-law, Andrew Farrow, said he attempted to return the book, among other police items left behind, to the RCMP. However, when the RCMP arrived to collect the documents, he says, the book had once again gone missing.

Andrew Farrow returns surveillance book to the RCMP. (CBC)

Last month, Farrow says the book was found again after it had been accidentally misplaced in boxes of Busch’s belongings.

Farrow said he called the general line at an RCMP detachment and was told to bring the documents into any RCMP office.

"I was very clear about it and they didn't seem to think it was too important," Farrow told CBC News.

"Now whether or not the other person at the end of the phone understood what it was, I'm not sure, and I didn't feel comfortable dropping it off at any detachment."

Book details Surrey Six suspects' movements

It appears that the surveillance notes in the book were made by Busch, who watched the movements of key suspects in the Surrey Six case between December 2008 to April 2009 as a member of the RCMP’s "Special O" team.

Six people, including two innocent bystanders, were gunned down in a high-rise apartment unit in Surrey in October 2007.

Six people have since been charged in the killings, including notorious gang member Jamie Bacon.

In addition, four RCMP officers are facing charges, including breach of trust, obstruction of justice and fraud, dating back to their handling of the Surrey Six slayings.

When CBC News contacted the RCMP to ask about the lost surveillance book, a spokesperson said such books were "personal notebooks" of officers, who are responsible for their safekeeping.

The RCMP said these books are used primarily to assist police officers with refreshing their memories when recounting his or her actions if called upon to testify at court proceedings.

But Farrow said he thinks such books shouldn't be brought home.

Police notebook containing detailed RCMP surveillance notes of Surrey Six suspects. (CBC)

"You don't just leave evidence out, it's mishandling of evidence in my opinion," he said. "You just don't leave it lying around, you just don't take it home, you don't take evidence home."

Criminologist Rob Gordon agreed, saying seemingly harmless observations can be crucial, in a case as important as the Surrey Six investigation.

"Even the most innocuous comment or observation may be of extreme value in the course of a later investigation," Gordon said. "You just don’t know."

Book returned to RCMP

Farrow brought the surveillance book to the CBC and was encouraged to try once again to return it to the RCMP.

This time, Farrow says an evidence clerk realized its potential significance, and the book was collected by the manager of the Surrey Six exhibits in August.

Gordon, the criminologist, said it's unlikely the book will have an impact on the upcoming Surrey Six case in court, but that the security breach is a major concern since the book contains the names of undercover officers as well as other potential suspects and witnesses.

As for Busch, he is no longer a member of "Special O" and CBC News has learned he now faces RCMP disciplinary action on numerous domestic abuse allegations.

Busch did not return calls from CBC News seeking comment.