A Calgary man stabbed his wife, two of his three children and a tenant to death before killing himself in his northwest home Tuesday night, police confirmed.

Insp. Guy Slater also said that defensive wounds on Alison Lall indicate she died trying to protect her two young daughters, Kristen, 5½, and Rochelle, 3½, from their father, Joshua Lall.

Simran Chandiramani, 5, centre, and her twin sister Aarti, pray with their mother Alka and Calgary Police Service Const. Andrew Fuhrman on Thursday after placing flowers on the front yard of the home where the bodies were found. (Jeff McIntosh/Canadian Press)

Slater said that it appears that Lall first attacked Calgary magazine writer Amber Bowerman, who was living in the Lalls' basement suite. Slater said it looked like she was taken by surprise because there was no sign of struggle.

Lall's body was located in the room of his one-year-old daughter, who was found crying in her crib, unharmed.

It's not clear why Lall did what he did.

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

There was no suicide note, no obvious warning and no evidence of drug or alcohol use.

But there are reports that Lall was under extreme stress, preparing for his accreditation exams to be registered as a professional architect while raising a family and holding down a full-time job at a Calgary architectural firm.

His father, Dominic Lall, told the Calgary Sun his son was distraught when he called his parents in Ontario a few days ago.

"He told us something was wrong — he had a mental breakdown or something," his father said. The couple was planning to fly to Calgary when they learned of the deaths.

Even so, Lall's colleagues, friends and neighbours describe him as a kind-hearted man who loved his family and was very involved in community activities.

Rochelle Lall, 3½, died along with her parents, her 5½-year-old sister and a tenant in their home. (CBC)

Rob Adamson, the chair at architecture firm Cohos Evamy, where Lall had worked for the past five years, said Lall shone at work designing buildings for the disabled.

"He was a very outgoing person in the project work he was doing," Adamson told CBC News.

Adamson said the job is high-pressure and deadline-driven, but "Joshua always seemed happy at work and interested in his work."

He said he last spoke to his employee on Friday, when Lall asked where he could take his wife for an 8th anniversary dinner. Adamson said Lall called in sick on Monday, and the day after called to request a week's holiday.

He said everyone at work wonders what led police to believe Lall could be responsible for the deaths.

"If that were in fact the case, it would be completely out of character and that's the biggest question on people's mind, is that it just simply doesn't make sense," he said.

Bowerman remembered as 'cheery and bright'

Meanwhile, friends and family are also mourning Bowerman, who had written for publications as diverse as Alberta Views and Calgary Real Estate News.

"Personally, I thought Amber was just a fabulous person," Colleen Seto, executive director of the Alberta Magazine Publishers Association, told CBC News.

"She always had a smile on her face. Always really positive and thoughtful. I can't imagine how her family are feeling right now."

Bowerman family spokesperson Ian Busby told CBC News the family is "devastated."

"It's hard to imagine this happening in anybody's family," he said.

"The troubling thing about how this is affecting everybody is she was one of those people that everybody sort of knows even if they don't know her by name. And they all know her as that wonderful person that's always, you know, cheery and bright."

He said Bowerman had described the home as a nice place to live, with a nice, normal family.