The first details about the inside of a north Minneapolis duplex where five siblings died in a fire in February were released Wednesday, showing where it likely started and how the children sleeping in the attic bedrooms were trapped.

The only stairwell leading to the attic was destroyed in the fire, leaving the children with no way to get out.

The state fire marshal's report reveals other tragic details: a dead dog's remains on the second-floor porch, a melted plastic playhouse in the living room and couches burned beyond recognition.

The report confirmed earlier indications that the fire started on the second floor of the upper duplex where Troy Lewis lived with seven of his children and laid out the duplex's floor plan. Lewis and two children, who all slept on the second floor, survived.

The report did not cite a cause but said investigators said the fire started in the living room, near where they found a "melted mass" that a lawyer for the family has indicated is a space heater. Shortly after the fire, Lewis told investigators a space heater he recently bought started the blaze.

The report had few answers as to precisely why the blaze began. Family attorney Jeff Sieben said the metal mass recovered by investigators will be fully studied in August by a number of experts who are participating in a joint private investigation.

"It has been X-rayed, but it hasn't been analyzed beyond that," Sieben said of the object, which possibly could include other melted items. "That's just a real preliminary piece of testing. There is going to be some extensive testing of it done."

Photos of the scene, released by the State Fire Marshal's Office, show melted couch springs and splintered wood strewn across the charred floor of the living room. What appears to be a pencil and some colored cloth can be seen embedded into the melted mass.

A previous Minneapolis Fire Department investigation said a space heater had been running in the archway between the living room and dining room.

It was in this approximate area, the northwest corner of the living room, where fire marshal investigators concluded that the blaze began. They did not directly implicate the melted mass, however.

Near the mass, investigators found a wall containing electrical conductors and metal electrical boxes among the debris. They were taken along with the object for investigation, according to the report.

Investigators also found an unplugged, "older-looking" space heater with a severed cord that was separated in the middle and knotted back together. No outlets were located in the vicinity of that space heater. The only item that appeared plugged in was an extension cord near the kitchen that ran from a living room wall to a nearby entertainment center.

The family who lived on the ground floor of the duplex escaped the early morning blaze. The third floor, where at least some of the five Lewis children were trapped, was divided into three bedrooms with mattresses. City officials have said the third-floor setup was legal. The report did not detail where the children had been sleeping the morning of the fire.

The floor was in good condition farthest from where the fire started one level down but partly burnt through on the other side. While the precise causes of death differed among the children, most suffered from smoke inhalation, according to the Hennepin County medical examiner's office.

In February, the Fire Department said that the cause of the fire was "undetermined." Assistant Chief Cherie Penn said in an e-mail this week that fire officials did not have any updates about the fire.

A spokeswoman for the State Fire Marshal's Office, Jennifer Longaecker, said her office does not typically comment or elaborate on its investigative reports because they assist in the investigation and are not the lead agency. The office is now monitoring the private investigation, which includes the family, property owner and insurance representatives, and involves experts from around the nation.

Sieben said the investigation is being monitored in the event what's learned can benefit others. "If we learn something that could save lives, it could benefit everybody in the state — and the country," he said. "

The family has sought to have a trustee appointed on behalf of the five children who died, a precursor to an anticipated wrongful-death lawsuit in several months. Sieben said the timing of that suit, and the number of defendants, will depend on the outcome of their investigation.

Eric Roper • 612-673-1732

Twitter: @StribRoper