Boston firefighters have discovered a second victim killed in a seven-alarm fire at a South Boston condominium complex, as investigators look into whether the blaze was deliberately set.

Fire Department spokesman Steve MacDonald said the body of an adult woman was found during a search of the building's remains Tuesday morning, as the Boston Herald reported that officials are investigating reports that two people were seen running from the house moments before the fire.

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No further information about the victim was available.

Peter Clancy, 47, died after he had a heart attack while being removed from the building during the fire Monday night.

The search for more victims was delayed until Tuesday morning, when a city building engineer determined the smoldering structure was safe for firefighters to enter.

MacDonald said that firefighters were continuing the search of the 18 unit complex early Tuesday afternoon.

Crews were ordered out about 45 minutes after they arrived at the 20-unit brick building shortly before 8 p.m., Deputy Fire Chief Joseph Finn said.

Officials had said the blaze apparently started in a first-floor kitchen at the rear of the building. Within minutes, flames spread to all five floors.

Flames shot out from the roof nearly three hours after the fire was reported, as some of the 130 firefighters sprayed water from ladders.

Residents of the apartment complex took shelter in a parked city bus, before being taken to a city recreation center. Boston Mayor Thomas Menino said many found shelter with friends and relatives.

The Associated Press contributed to this report.