The RCMP never considered anyone else as suspects in the brutal killings of two people east of Edmonton four years ago other than two 14-year-old boys, RCMP admitted Tuesday.

Trudel, 50, and Boenke, 68, were found bludgeoned and shot to death , in what police described at the time as "random" murders, on an acreage near Ardrossan, east of Edmonton in June 2009.

Just hours later, police arrested two 14-year-old boys who were wards of the province and had gone missing hours before from the nearby Bosco Homes facility for troubled teens.

Despite a video entered as evidence Tuesday showing a ghastly and blood-splattered crime scene, no forensic evidence, such as DNA evidence, fingerprints, bloody clothing or murder weapons, was ever found to link the teens to the crime.  

In the end, police were forced to rely on evidence from a police interview with one of the boys in order to lay charges, but the case fell apart in July 2011 when the videotaped interview was declared inadmissable by a judge. 

Sgt. Jason Reeve, the lead investigator, told the trial Tuesday that one month after the charges were suspended, RCMP decided at a high-level meeting to continue the investigation.

For nine months, Mounties used surveillance, wiretaps and an undercover investigation often referred to as a "Mr. Big sting operation."

The sting involves an undercover officer who portrays a crime boss in an attempt to gain a confession recorded by a hidden camera.

In the end, police were able to lay murder charges against only one of the teens.

In cross examination, Reeve admitted they've never considered anybody else as a suspect and all investigators efforts were aimed at the boys.

The boy, who was originally charged as a co-accused but released when the case initially fell apart, will also testify for the Crown later this month.

The trial is scheduled to last six weeks.

With files from CBC's Janice Johnston