Redmond Fire Department investigators have officially ruled the cause of the fatal New Year’s Day apartment fire as “undetermined.” But investigators were able to determine that the fire was not caused by cigarette or marijuana ashes, according to the city’s assistant fire marshall.

This week’s announcement ends a nearly one-year thorough investigation of the fire that broke out on a ground-level unit at the Sammamish Ridge Apartments and took the lives of a beloved father and his four sons.

“It’s frustrating, but that’s where we are at,” Assistant Fire Marshall Lynn Sjolander said Tuesday morning of the investigation’s findings. “It’s a process of elimination and we determined, it’s  undetermined.”

David Thompson and his four sons — ranging in ages from 2 to 12 — died from smoke inhalation after flames engulfed Building 3 of the apartment complex at 14820 Redmond Way, at around 2:30 a.m. Jan. 1. Thompson’s wife, Lily Reasor, was the only one from the family to survive.

While the cause of the fire is unknown, investigators were able to eliminate a scenario — reported by the Seattle Times in a Jan. 2 story — that the fire was caused by cigarette or marijuana ashes, Sjolander said.

“We ruled that out,” he said. “That didn’t play into the cause at all.”

Investigators also ruled out any sort of electrical malfunction caused the fire, Sjolander said. Redmond Fire investigators recently received the testing results from wiring and electrical outlets sent to the Federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) Forensics Laboratory in Maryland that determined the electrical samples were not the cause of the fire. The electrical samples taken from the wall by the master bathroom — where the fire started, according to Sjolander — was the last piece of evidence to be examined, Sjolander said.

Other pieces of evidence were sent to the Washington State Patrol Crime Lab, where many causes were eliminated, but no one concrete cause could be determined, Sjolander said.

“We appreciate the efforts of all agencies outside of Redmond who were part of this response including the ATF, Washington State Patrol, and Seattle Police,” Sjolander said. “Our thoughts are with everyone affected in this situation including the family, friends, residents, staff, and first responders.”

Sjolander, who met with apartment staff on Monday, commended the “strong sense of community” the apartment complex staff members and residents have shown in the wake of the tragic fire. He said the apartment community “bonded together like a family.”

Teresa Lunsford, the apartment resident manager, said she is thankful for the efforts of investigators, including the Redmond Fire and Police Departments.

“Not knowing (the cause of the fire) is strange, but I’m settled with that,” she said Tuesday. “The evidence was handled in the most professional way. We are happy we are at this point.”

But even though the investigation is over, the memories of that tragic night remain for Lunsford, who lives at the apartment complex, and other residents who were there the night of the fire.

“This has been a hard year,” Lunsford said. “This has forever changed my life,” she said.

Lunsford said she has watched first hand the demolition of the once-charred Building 3 from her office window. The building is currently being re-built from the garage up and should be open for rent by mid February, Lunsford said.

Lunsford said Thompson, along with his four sons, Tristan, 12, David Jr., 6, Leviticus, 4 and Wyat, 2 were a fun-loving bunch and good neighbors. She said Thompson worked as a maintenance assistant at the apartment complex and was a family-first man.

Lunsford periodically talks to Reasor, who now lives in Colorado with other family members and Lunsford said “she’s doing the best she can.”