A crime scene video of a double murder was too much for the victims' families in an Edmonton courtroom Monday.

The video was shown to the judge on the first day of the second-degree murder trial of a 17-year-old in the brutal killings of Barry Boenke and Susan Trudel four years ago.

One man ran sobbing from the courtroom while Boenke's sister Gerlind Koesling sat quietly wiping away tears as the video played, a video she's seen before.

"Susan's head was bashed in," she said. "I knew my brother had three bullet wounds in him."

Nevertheless, it's been a day Koesling has been waiting for a long time now.

"It's not easy. He was my big brother. Now I don't have him."

Trudel, 50, and Boenke, 68, were found bludgeoned and shot to death on her acreage near Ardrossan, east of Edmonton, on June 1, 2009.

The suspect was a 14-year-old ward of the province living at the Bosco Homes facility for troubled teens in Strathcona County at the time of the slayings.

He was charged along with another boy hours after the bodies were discovered, but the Crown stayed proceedings in July 2011, the case falling apart when a judge refused to allow a videotaped statement from one of the boys into evidence.

"I can't express how sad it made us when everything was thrown out the first time," said Koesling.

"Really we were hurt more than anything else — as if my brother was never here. And same with Sue."

However, charges were reactivated against the other teen last year.

The court was told Monday that evidence gathered as part of an undercover tactic known as a "Mr. Big" sting will make up part of the Crown’s case.

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

Koesling said she's glad Mounties went what she called "the extra mile."

"I'm very happy that they did that," she said.

The boy, who was originally charged as a co-accused, will also testify for the Crown later this month.

The trial is scheduled to last six weeks.

With files from CBC's Janice Johnston