A total of three people have now been charged with first-degree murder in the death of Saskatoon's Lorry Ann Santos earlier this year.

Santos was a 34-year-old mother of four who police said had answered a knock at her door and was shot dead.

Randy James Wayne O'Hagan has been charged with first-degree murder in the deaths of Lorry Ann Santos, Bryan Gower and Robert John Roth Sr. (Facebook)

On Tuesday, a day after Kyle Darren Halbauer, 22, of Lloydminster, Alta., appeared in court, charged with first-degree murder, the Saskatoon Police Service announced that Joshua Dylan Petrin, 29, of Edmonton and Wayne O'Hagan, 22, of Lloydminster, were also being charged with the same offence.

In addition to the Santos homicide, Halbauer and O'Hagan are also charged with the death of Bryan Gower, 35, on Sept. 25, 2012. Gower's body was discovered on a rural road near Kitscoty.

O'Hagan and a fourth man, Nikolas Jon Nowytzkyj, 32, of Wainwright, Alta., have been charged with the murder of Robert John Roth Sr. of Lloydminster. Roth's partial remains were found near Ranfurly, Alta. on Oct. 20, 2012. His severed head was discovered in Edmonton five days later.

Police said the incident at Santos' home was the result of cross-border drug dealing and organized crime.

Investigators believe an Alberta gang, White Boy Posse, was attempting to make inroads into Saskatoon's illicit drug trade and was trying to intimidate people in the city.

Kyle Darren Halbauer is charged with first-degree murder in the deaths of Lorry Ann Santos and Bryan Gower. (Facebook)

But Santos and her family were innocent victims who had no connection to that activity, they said. Instead,

"It was a wrong address," Insp. Jerome Engele told a news conference.

Police said more than 100 officers in Alberta and Saskatchewan were involved in the investigation. They also thanked the Santos family, Saskatoon's Filipino community and the neighbourhood for their patience while the investigation was underway.

Halbauer made his first appearance in Provincial Court on Monday.

Petrin is scheduled to appear in Provincial Court at 2 p.m. O'Hagan is in custody in Edmonton, with a court appearance date yet to be released.