BOSTON (CBS) – The medical examiner has released the official cause of death for two Boston firefighters killed in a fire on Beacon Street in March.

Lt. Ed Walsh and Firefighter Michael Kennedy both died of smoke inhalation and thermal injuries, according to the medical examiner’s report.

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Their deaths have been ruled accidental.

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The District Attorney’s office is still investigating the fire. They believe sparks from a welding crew working next door caused the blaze.

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