INDIANAPOLIS (AP) — The house explosion that killed two people and destroyed several homes in an Indianapolis neighborhood is now a homicide investigation, authorities said, though no suspects have been named.

Indianapolis Homeland Security Director Gary Coons made the announcement Monday evening, shortly after a funeral was held for the husband and wife who were killed. The couple lived next door to the house where investigators believe the blast occurred.

"We are turning this into a criminal homicide investigation," Coons said after meeting with local residents, marking the first time investigators have acknowledged a possible criminal element to the Nov. 10 explosion.

Search warrants have been executed and officials are now looking for a white van that was seen in the subdivision the day of the blast, Marion County Prosecutor Terry Curry said. Federal authorities are offering a $10,000 reward for information in the case.

Curry said the investigation is aimed at "determining if there are individuals who may be responsible for this explosion and fire," but neither he nor Coons took questions or indicated if investigators had any suspects. No arrests have been made.

Officials have said they believe natural gas was involved in the explosion, which destroyed five homes and left dozens damaged, some heavily. Investigators have been focusing on appliances as they search for a cause of the explosion, which caused an estimated $4.4 million in damage.

"We thought something like this was not just an accident," said Doug Aldridge, who heads the neighborhood Crime Watch.

Aldridge said he and other residents frequently saw a white van parked outside the home, though he didn't know who owned it. He said residents were angry and upset, but he expects most of them to stay in the neighborhood.

"Everyone had their suspicions," said Chris Sutton, who lives a street away from the blast site.

"It's kind of scary that someone might set off a gas explosion," he added. "It's really scary."

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Hundreds of people attended the funeral earlier Monday for the couple killed in the explosion, 34-year-old John Dion Longworth and 36-year-old Jennifer Longworth.

She was a second-grade teacher remembered for knitting gifts for her students, while her husband, an electronics expert, was known as a gardener and nature lover. The school where Jennifer Longworth taught was closed Monday so teachers and students could attend the funeral.

Indianapolis Mayor Greg Ballard, who spoke at Monday's news conference, said he went to the Longworths' funeral and had a hard time coming to peace with what had happened.

"There is a search for truth and there is a search for justice," Ballard said.

The couple lived next door to the house where investigators are focusing.

The co-owner of that house, John Shirley, told The Associated Press he had recently received a text message from his daughter saying the furnace in the home, which she shares with her mother and her mother's boyfriend, had gone out.

Shirley's ex-wife, Monserrate Shirley, said her boyfriend, Mark Leonard, had replaced the thermostat recently and the furnace had resumed working.

She and her boyfriend were away at a casino at the time of the blast. The daughter was staying with a friend, and the family's cat was being boarded.

Monserrate Shirley's attorney, Randall Cable, declined comment Monday night.

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Associated Press writer Ken Kusmer contributed to this report from Indianapolis.