James Bing Jun Louie, 43, is taken to the arrest processing unit by Calgary police on Saturday. (Courtesy Calgary Sun)

The mother of two children found dead in their Calgary house called 911 as she was driving home, expressing concern for their safety, but the dispatcher determined there was no imminent threat.

When she called back a half hour later from the house, only a scream could be heard before the line went dead.

The children's father, James Bing Jun Louie, has been charged with two counts of first-degree murder. The charges were upgraded on Monday from second-degree murder, suggesting prosecutors feel the crime was premeditated.

He is also charged with one count of attempted murder related to a physical altercation involving his wife.

Louie, 43, said nothing during his first, brief appearance in provincial court via closed-circuit television Monday. He was remanded in custody until his next scheduled court date Dec. 14.

Louie was arrested Friday night after Calgary police responded to an emergency call at a house in the northwest neighbourhood of Panorama Hills.

Louie's wife, Ying Louie, called 911 on her cellphone at 8:33 p.m. as she was driving home, because she couldn't reach her children, said Calgary emergency officials on Monday.

Two children were found dead inside this northwest Calgary home. Their father has been charged with two counts of first-degree murder. (Bryan Labby/CBC)

During the call, which lasted eight minutes, the operator went through a series of routine questions for that type of situation and determined the children were not in imminent danger, said Steve Dongworth, manager of public safety communications for the city.

The dispatcher told Ying Louie to call back if she found something amiss at home. When a second 911 call was placed at 8:59 p.m., only a scream could be heard, said Dongworth.

It took police 16 minutes to reach the house from the time of that second call, because they had to first trace where the call came from, and then officers battled extremely icy road conditions to reach the home.

Calgary police Insp. Guy Slater said the children had been killed before their mother's first 911 call.

Dongworth said the 911 operator on the first call followed proper protocol.

No weapons removed from home

On arriving, police forced their way into the home and found the body of 13-year-old Jason Louie and following a search of the house, that of his nine-year-old sister.

When officers arrived, the parents were engaged in a physical struggle. Police intervened and took Louie into custody, preventing, they said, a third homicide.

The children's mother was taken to hospital with non-life-threatening injuries.

Defence lawyer Noel O'Brien had no comment Monday on the state of Louie's mental health.

"I'm going to wait until I get the facts from the Crown," O'Brien said, adding he expects the Crown to disclose all relevant facts to the defence within a few weeks. "And once we get that, we'll make our assessment with respect to his mental competence and things of that nature.

"It's a very tragic situation. They really do need privacy in this scenario."

Police said an autopsy on the bodies of the children was completed but that the results would not be released at this time. Slater added that no weapons were removed from the home.

Peers, teachers mourn victims

Grief counsellors were on hand Monday at the two Calgary schools the Louie children attended to help students deal with the loss of their friends.

Friends posted photos and videos on a memorial Facebook page for Jason Louie, 13.

Staff and students at Sir John A. Macdonald High School and Alex Munro school were having a hard time absorbing the sad news, said Ted Flitton, a spokesman with the Calgary Board of Education.

He said critical-incident response teams were at the schools to try to help counsel those — including staff — who were in distress.

"The idea is to monitor the staff and students, circulate in the halls, be present, make sure you're making eye contact, and checking in with people and just making sure that people are OK," Flitton said. "And if they're not … engage them in a conversation. They're certainly very upset today."

One of Jason Louie’s classmates said Jason was active in sports and liked by all.

"He was a good guy, really nice to everyone," she said. "I talked to him on the first day, and he showed me the class.

"We're spending time today writing about him. Everybody is sad; everybody is crying."

Friends of Jason Louie started three Facebook pages on which they shared condolences and memories of the teen, who reportedly enjoyed soccer and track and field.

With files from Zulekha Nathoo and The Canadian Press