A Calgary man stabbed his wife, his two young daughters and a basement tenant to death before taking his own life, police have confirmed.

The horrific details of a multiple homicide that shook the nation this week were released by police late Friday night.

Autopsy results showed Joshua Lall, 34, his wife Alison, 35, daughters Kristen, 6, and Rochelle, 3, and tenant Amber Bowerman, 30, all died of multiple stab wounds from one knife which police retrieved from the crime scene.

Calgary police Insp. Guy Slater said defensive wounds on Alison Lall suggest she died trying to save her children.

"Every indication is that Alison fought to protect her children," said Slater.

Slater also told reporters that evidence shows the attack was orchestrated by Joshua Lall on Tuesday night. The bodies were discovered on Wednesday.

Only one person remained alive in the house after the slayings -- one-year-old daughter Anna, who was unharmed, and whose crying prompted the discovery of the bodies.

Police say they found Joshua Lall's body on the floor in Anna's room.

Tenant was killed first

Police claim Bowerman was killed first, and was likely taken by surprise. Police said there were no signs of a struggle in the tenant's basement apartment.

"There is nothing to indicate that Amber could have done anything in her situation," said Slater.

The man then went upstairs to the master bedroom where he killed his wife and two young daughters, before taking his own life.

There are still many questions police are trying to find answers to, said Slater, "and some information we are not going to make public."

While police were able to say how the family was killed, they couldn't explain why.

"I can't even speculate on that," said Slater. "The only person that knows that is Joshua himself."

Slater said there were no initial signs that drugs or alcohol were involved. But media reports in Calgary have suggested that Joshua Lall was struggling with an unspecified mental illness.

"There was information provided by the family, and that is being considered in the totality of the investigation," said Slater. "However, again, it will be up to mental health experts to make a determination."

The deaths have shocked the community. Those who knew the Lalls have said there were no obvious indications that would have led them to think such a tragedy was possible.

Vigil for family

The grieving community continued to pay its respects on Friday, as a memorial of flowers and stuffed animals grew at the Lall home.

"I just wanted to acknowledge the relatives and friends and show that everyone is thinking of them at this difficult time," resident Greg Parsons told CTV Calgary.

"I wanted to show my respect to the children, the mother and even to the father, because I don't believe he was in his right mind," added resident Lisa Sangregorio.

A Calgary church planned a candlelight vigil Friday night for the victims.

"This is a Christian family, and this is a Christian community," CTV's Rob Brown told Newsnet from Calgary.

"As is so often the case in these murders -- where you have a family involved and children are involved -- it affects people far and wide."

The victims' bodies were found scattered throughout various rooms of the house.

A family acquaintance arrived at the home Wednesday morning and found the bodies of the girls, three-year-old Rochelle and six-year-old Kristen, and the three adults.

Police earlier said they are investigating reports that Joshua Lall had called his parents days before his death to say he was suffering some kind of mental breakdown.

Police had not been called to the house for any previous domestic incidents.

It was also revealed Thursday that Lall wasn't missed at work on the day his body was found because he had a "planned absence."

Shocked neighbours described Lall as a "loving" father, and former teachers recalled the valedictorian as an exemplary student.

With a report from CTV Calgary's Sue French