An investigation into a house fire in Calgary earlier this month has turned into a possible sexual assault investigation.

A woman in her 50s was taken to hospital after a basement suite in Sunnyside caught fire in early October.

She was in critical condition with facial injuries, second-degree burns and smoke inhalation.

Police say once she was able to speak, and when they received the full medical reports, the focus shifted to a possible violent sexual assault.

Staff Sgt. Mark Hatchett says police have a suspect in custody — a man known to the woman.

"We are currently investigating the nature of the relationship," he said. "At this time we believe it's a casual relationship of some sort and didn't amount to more than a couple days." 

He says officers are interviewing the man today but no charges have been laid.

Investigators are trying to determine if the fire and the alleged assault are connected. Police say the fire was not an accident.

The woman has since been released from hospital.