St. Joseph, Mo. ? Foul play has been completely ruled out in an August house fire that killed six family members, St. Joseph police and fire officials said.

An electrical problem is to blame for the blaze, they said Friday in announcing that their investigation is closed.

Fire Inspector Steve Henrichson said a cord in a window air-conditioning unit showed signs of electrical arcing, which he believes was the source of the fire.

The family dog and its new puppies had a bed near the air-conditioning unit, and one of the puppies could have damaged the cord, Henrichson said.

Police Detective Richard Shelton said the fire was “nothing more than a tragedy and a really, really tragic accident that cost six people their lives.”

“We have a husband that’s going to have to live with some things for the rest of his life,” Shelton said.

Bryan Riggs, 39, survived the Aug. 11 fire by jumping out a second-floor window. His wife, Lisa Riggs, 38, was killed along with their sons, Kealan, 8, and Tristan, 11.

The other victims were: 16-year-old Sean Fox, who was Lisa Riggs’ son from a previous marriage; Patricia Duryee, 61, the mother of Lisa Riggs; and Brandon Lee Updegraff, 10, the nephew of Lisa Riggs.

The fire was largely contained on the first floor in the living room area. However, much of the house had smoke damage.

All six victims were found in a second-floor bedroom. Police said Friday that Jackson County medical examiner investigators determined they all died from smoke inhalation.

Investigators said one piece of the incident that they will never know is why the victims stayed upstairs. They said Lisa Riggs called 911 from her cell phone.

“The six people who know that answer are no longer with us,” Detective Shelton said.

One other family member survived the blaze – Lisa Riggs’ 17-year-old son Brandon Fox. Relatives have said he was staying at a friend’s house at the time of the fire.

Shelton said Bryan Riggs told police his wife woke him up, but that it took him a minute or two to realize what was happening. Riggs told investigators that he left the house thinking the others had made it out safely.

Riggs was inside the house when the first police officer reached the scene. Shelton said he apparently had gone back in looking for his family.

“I believe that if our officer hadn’t gotten there, (Riggs) wouldn’t have come out of that house,” Shelton said.