PITTSBURGH (KDKA/AP) — Investigators say smoking caused the fatal fire at the Midtown Towers in Downtown Pittsburgh earlier this month.

They say the victim, 75-year-old Mary Robinson, was likely smoking in or near her bed when it caught her sixth-floor apartment on fire.

Two other residents were hurt, but survived. Three firefighters also suffered minor injuries in the fire.

Two firefighters became trapped on the seventh and eighth floors while battling the blaze, which prompted two mayday calls.

The fire reached seven alarms in the early morning hours of May 15 at the 17-floor apartment building.

All residents were evacuated and are now staying elsewhere. Last week, groups of residents were allowed back inside to salvage belongings. It’s unclear when they can return to stay.

Authorities say the building’s fire alarm did function, alerting emergency personnel to the blaze.

However, Pittsburgh Fire Bureau officials said it was a difficult fire to fight because the building did not have a sprinkler system.

Chief Darryl Jones has since called for more buildings to be required to have sprinkler systems. Currently, only city high-rises built after 1990 or those undergoing major renovations are required to install such systems.

Stay with KDKA for the latest on this developing story.

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(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)

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