VANCOUVER -- The nephew of one of the two innocent bystanders killed in a gangland execution says he heard several loud bangs around the time prosecutors believe six men were executed in a nearby suite on the 15th floor of a Vancouver-area high rise.

But Zach Brown, who was working with his uncle to service gas fireplaces in the Surrey complex on Oct. 19, 2007, acknowledged during testimony Wednesday that he couldn't say just what the noises were, and he initially told police he didn't think it was the sound of gunfire.

Brown, who was 20 at the time, was working for his father's gas fitting company alongside his uncle, Ed Schellenberg. Brown and Schellenberg had divided up the work, with Brown in unit 1508 while his uncle serviced 1505.

It was in unit 1505, down the hall and around the corner from where Brown was working, where Schellenberg, building resident Chris Mohan, and four men with ties to gangs and drugs were gunned down in what the Crown alleges was a gang-related hit.

Brown said he was servicing the gas fireplace in 1508, chatting with a man named Robbie who lived there, when he heard several loud noises off in the distance.

"We were having a conversation and I heard four or five steady noises that were sort of a background noise -- I sort of passed it off, didn't want to interrupt the conversation," Brown testified at the trial of three alleged gang members charged in the mass killing.

"They were very steady and grouped together. There was no pause between each sound, it was one, two, three, four, five."

Brown was presented with a floor plan of the condo building and he indicated the sound came from the southeast -- the same general direction as suite 1505.

Brown said he couldn't say, then or now, what caused the sounds, though during a police interview in the hours after the shooting he described what he heard.

"I do remember hearing something and it sounded like banging, I think, but I passed it off as nothing right away, just because it sounded like someone dropped something," he told a police investigator, according to a transcript that was read in court.

"And it was four or five -- boom, boom, boom, boom -- and that was it. ... It didn't sound like gunshots, though; it wasn't loud enough. It just sounded like hitting on the wall."

Matthew Johnston, Cory Haevischer and Quang Vinh Thang (Michael) Le are now on trial for various murder and conspiracy charges. A co-accused has already pleaded guilty and another, alleged gang leader Jamie Bacon, is scheduled for trial next year.

The Crown alleges Johnston, Haevischer and a third man, who can't be named, went to the condo to execute drug rival Corey Lal. The Crown alleges five more were killed, including Schellenberg and Mohan, to eliminate potential witnesses.

The exact timing of the shooting will be important as the trial unfolds. The Crown's theory has the alleged attackers arriving at the complex at about 2:20 p.m. and leaving roughly 25 minutes later, providing a short window for the shooting to have occurred. The building's manager didn't enter the unit to discover the bodies until sometime after 4 p.m.

Defence lawyers cross-examining Brown focused on the young man's own doubts about what the noises were.

The shooting killed Schellenberg, 55, and Mohan, 22.

The other victims were Corey Lal, who the Crown contends was the intended target of the shooting, Lal's brother Michael, Edward Narong and Ryan Bartolomeo.

Johnston and Haevischer are accused of being directly involved in the killing, along with another man who cannot be named, while Le is accused of being part of the conspiracy.

Alleged gang leader Jamie Bacon is also charged in the case, though he is scheduled to stand trial separately next year.