An electrical engineer from the Ontario Fire Marshal's office has been investigating the cause of a fatal apartment fire on Thornberry Crescent in Windsor.

Damage is estimated at $275,000.

Martin Bossom, 30, died of his injuries and his 21-year-old girlfriend, Samantha Stanley, remains in critical condition.

The electrical engineer is looking into whether wiring inside the building may have started the fire. The investigation is expected to continue Tuesday.

Meanwhile, friends and family members are making funeral arrangements for the young father.

Bossom died on Saturday at Windsor Regional Hospital, surrounded by friends and family.

“I was having so much hope maybe a miracle would happen, but I guess it was his time,” says Heather Stanley, Samantha’s sister.

Samantha Stanley remains in a medically induced coma in a Hamilton hospital. Her sister says she's getting stronger every day.

“It's gonna take a long time, a lot of fighting but she is ok,” she says.

Stanley says her sister has first and second degree burns on her face and chest, but is no longer in an oxygen chamber.

Firefighters pulled the couple from the apartment building after fire broke out early Friday morning.

“We're making sure wiring in that area will be confirmed as the source of fire or ruled out,” says Windsor’s chief fire prevention officer Lee Tome. “So at this point, still no cause.”

Tome says part of the investigation will be to try and determine whether or not there were working fire alarms inside the apartment.

Heather Stanley says her sister and Bossom were planning to start a family together. But now, the focus will turn to Bossom's six-year-old son, Damian, who friends say was the love of his life.

A trust fund has been set up for Samantha Stanley at Scotiabank. Her sister says the money will be for ongoing medical expenses and to help her get back on her feet since she lost everything she owns in the fire.