Sheriff’s Office rules fire deaths were murder⁄suicide

Cpl. Jennifer Bailey, a spokeswoman for the Frederick County Sheriff’s Office, said investigators ruled that Marijke McMahon died of blunt-force trauma to the head and asphyxiation. ‘‘It is believed that he murdered his wife and set the fires prior to hanging himself,” Bailey said. Court records show that Marijke McMahon filed for divorce on Oct. 3. The couple had 3-year-old twin daughters, who were not in the house at the time of the fire. Relatives are caring for them.

Bailey said the Sheriff’s Office had responded to a domestic assault at the McMahon home on at least one occasion, but would not provide details. The fire was ruled an arson, with separate fires started on each level of the house, according to the Sheriff’s Office. Investigators believe Sean McMahon used a chemical accelerant to start the fire, the presence of which was confirmed by a dog trained to detect accelerants, and sent samples of the liquid to the Maryland State Police Crime Lab for tests.

According to the Sheriff’s Office, two adjoining townhouses were spared damage from the fire because of firewalls between them. The Maryland State Fire Marshal’s Office and the Frederick County Sheriff’s Office are both investigating the fire, with assistance from the Frederick County Department of Fire and Rescue Services.

More than 100 emergency personnel responded to the fire Thursday night, including firefighters from Montgomery, Carroll and Frederick counties.

Anyone with information is asked to call Cpl. Jason West of the Sheriff’s Office, 301-600-3894.