A special prosecutor has recommended charges against four Mounties connected to the investigation of a B.C.'s worst-ever gangland killings, that left six people dead in Surrey, B.C.

The officers face a combined 20 counts, including charges of breach of trust, obstruction of justice, fraud and compromising the safety of witnesses in investigating the so-called "Surrey Six" slayings.

Derek Brassington, David Attew, Paul Johnston and Danny Michaud are scheduled to appear in court on July 11 in Vancouver.

The officers, who have all been suspended with pay, also face a separate internal RCMP code-of-conduct investigation.

The charges were approved by Christopher Considine, a Victoria lawyer appointed by B.C.'s criminal justice branch in March to examine allegations of a sexual relationship between a sergeant investigating the murders and a witness.

The Surrey Six murders were committed in a high-rise apartment unit in October 2007. Two innocent bystanders, 22-year-old Chris Mohan and 55-year-old gas fitter Ed Schellenberg, were among the victims.

Police say both were simply in the wrong place at the wrong time.

James Kyle Bacon, quang Vinh Thang Le, Matthew James Johnston, Cody Rae Haevischer, Dennis Karbovanec and Sophon Sek have all been charged in the slayings.

Karbovanec pleaded guilty in April 2009 to three counts of second-degree murder and conspiracy to commit first-degree murder in the slayings.