Detectives also discovered a fourth body in another home, matching the social media post apparently written by Randy Janzen last Thursday.
"We believe them to be the family — the three members of the Janzen family — as stated in the Facebook posting by Randy Janzen," said Sgt. Stephanie Ashton of the Integrated Homicide Investigation Team on Monday.
Janzen's post says he shot his daughter Emily to relieve her of excruciating migraines, and then turned the gun on his wife Laurel and sister Shelly.
The post says: "Over the last 10 days I have done some of the worst things I could have ever imagined a person doing."
Ashton said detectives are waiting for the B.C. Coroner's Service to confirm identities. Coroner Barb McLintock couldn't say how long the analysis will take.
Ashton asked members of the public to help officers as they build a timeline of the deaths.
"Any kind of contact — even a small Facebook posting or social message — we're interested in hearing from people that communicated with anyone from the Janzen family from about mid-April to May 7."
Police were first alerted to a potential triple homicide by information received from social media last Thursday afternoon.
Officers were dispatched to a home in Langley, B.C., where they found the first body. A long-time friend has said the home belonged to Shelly Janzen.
They were then led to a second location in the Rosedale Popkum neighbourhood of Chilliwack, east of Vancouver.
A four-hour standoff ensued with a man, before the home caught fire and was quickly engulfed in flames.