Updated:LOWELL, Mass. (MyFoxBoston.com) -- Middlesex District Attorney Marian Ryan said she expects the investigation into the state's deadliest fire in two decades to be a long and thorough process.
Seven residents died when a fire broke out at an apartment building on Branch Street in Lowell early Thursday morning. A woman and man were found dead in one unit on the top floor. A family of two adults and three children were in another.
Authorities believe the fire started on either the second or third floor of the building. Approximately 50 people were inside at the time.
Witnesses said they heard what sounded like fireworks exploding. Several people jumped from windows and at least one child was dropped to safety.
Nine people were taken to the hospital with serious, but non-life threatening injuries. Dozens of people were displaced.
The investigation will continue through the weekend, with the focus continuing on witness statement analysis and scene examination.
Authorities are still looking into the cause of the fire and whether the fire alarms were working. Officials say the building did not have a sprinkler system and wasn't required to. It was built in 1890 and grandfathered into city code.
The Lowell Director of Development Services told FOX 25 the building was inspected last spring and did have working carbon monoxide and smoke detectors in every unit at the time. Another inspection was set for 2016.
The city of Lowell plans to demolish the building for safety reasons. That won't happen for a few days until investigators from the state fire marshal's office can finish collecting all the evidence they need.
The city has set up a fund for victims. Donations can be sent to the Jeanne D'Arc Credit Union for the "The Branch Street Fire Victims Relief Fund." The American Red Cross said clothing and other items can be donated to the Wish Project.
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