Investigators trying to determine how last week’s fatal fire started in a Northwest Washington rowhouse that officials described as an illegal rooming house are focusing on an electronic device and a power cord, according to court documents.

An application for a search warrant filed in D.C. Superior Court says police and federal agents took those two items from the charred remains of the dwelling at 708 Kennedy Street NW, which officials said lacked approval for rental units and functioning smoke detectors.

An electrician with the Bureau of Alcohol, Tobacco, Firearms and Explosives is examining the items, which are not detailed in the court documents, but authorities said a cause of the Aug. 18 fire has not yet been determined. Fitsum Kebede, 40, and Yafet Solomon, 9, a student at Barnard Elementary School, were killed in the fire.

Yafet lived at the house with his mother and was buried Wednesday. Kebede has family in Ethi­o­pia and a sister in South Africa who are applying for visas to visit the United States and make funeral arrangements.

District officials said a multipronged criminal investigation led by federal prosecutors is underway into the cause of the fire and the conditions in which people lived inside the house, which was licensed as an online pharmacy. The officer who filed the search warrant is assigned to the department’s homicide unit and is on a task force that investigates serious fires.

The owner of the rowhouse, James G. Walker, has not responded to interview requests, including Thursday.

Officials also are investigating what they said are failures by the city in responding to a police officer’s March warning about numerous “life-safety violations” he noticed during a routine call to the location in March.

Inspectors with the Department of Consumer and Regulatory Affairs and the Fire and Emergency Medical Services failed to appropriately act on the warnings, officials said.

Tenants — Ethio­pian immigrants — have said the first and second floors and basement were partitioned into a dozen rooms, some no larger than a queen-size mattress, with communal kitchens and bathrooms. Renters said they paid between $300 and $650 month.

Officials have described a maze of corridors, and police wrote in the search warrant that some areas were built with 2x4 lumber and drywall that were “not consistent with proper living quarters, safety guidelines or building codes.”

Police and the fire chief previously have described how an officer first noticed the fire and tried to get into the house but was stymied by metal bars on the front door. Two officers and bystanders got the bars off but were forced back by smoke. One woman escaped from the top floor by following the officer’s voice.

The search warrant says firefighters who went inside encountered a second solid-wood door 10 feet into the interior. They forced that open and then found a locked metal gate that also had to be broken down. Firefighters found the man and child unconscious in the basement, where authorities believe the fire began.

The officer who was inside the house in March wrote in a report that he noticed “make shift doors with locks which would make it difficult to exit in an emergency.” Several officials who are familiar with the body-camera video from that officer described the layout as complex and confusing.

In the search warrant application, the detective told the judge investigators planned to “create a sketch, take additional photographs and determine occupancy of each of the rented ‘bedrooms.’ ”