A B.C. man has pleaded guilty to three counts of second-degree murder and three of his alleged gang associates have been arrested in connection with a bloody shootout which killed six people in 2007.

Four men with criminal ties were killed during the incident, along with two innocent bystanders caught in the crossfire at a Surrey, B.C., apartment building.

The brutality of the deaths sent shock waves through the Lower Mainland and marked the start of a violent chapter in the province's battle against organized crime. Since then, there have been 100 shootings in the region, many of them deadly.

On Friday, Dennis Karbovanec, 27, pleaded guilty to a trio of murder charges and also admitted to one count of conspiracy to commit murder for his part in the Surrey killings. His arrest and the charges against him were not previously announced by police.

Karbovanec admitted to murdering Chris Mohan, a 22-year-old innocent bystander who lived in the building where the slayings took place and was accidentally caught in the crossfire.

Karbovanec's other victims were Ryan Bartolomeo, 19, and Michael Lal, 26 -- two young men police say were linked to the criminal underground.

The other innocent victim, Ed Schellenberg, was a 55-year-old father of two who maintained the tower's fireplace system.

Corey Lal, 21, and Edward Narong, 22, two men police said also had criminal backgrounds, were killed.

Meanwhile, officers arrested three of Karbovanec's alleged criminal comrades -- James Kyle Bacon, Matthew James Johnston and Cory Ray Haevischer -- for conspiracy on Friday.

Police believe that Bacon is linked to the Red Scorpians gang, which is locked in a deadly turf war with the UN gang. Bacon survived an apparent attempt on his life earlier this year.

All six bodies were discovered by a haz-mat team after neighbours complained about a smelly, gaseous odour in the building.

"It was a very horrific time in the Lower Mainland," said the Integrated Homicide Investigation Team's Cpl. Dale Carr early Friday afternoon.

In a short news conference, Carr added that other arrests linked to the killings were expected to be announced.

"I can tell you that as we speak right now, there are additional arrests that are taking place and there will be additional arrests throughout the weekend in connection to this file."

Carr added that more details about the case will be released on Saturday.

Karbovanec, who was arrested on unrelated fraud and possession of stolen property charges, has been the subject of rare police warnings for the public.

With files from The Canadian Press