The explosion that destroyed a house in suburban Dallas earlier this week and heavily damaged the two next door, injuring six people, may not have been an accident, officials say.

Previously, fire officials had said that a gas leak in the Plano home that was destroyed Monday was the likely cause of the explosion.

“After further investigation, it was determined the explosion may have been intentional,” Plano Police and Plano Fire-Rescue said in a news release, without providing details.

It appeared to be an isolated incident with no indications of any threats to the community, and the investigation remains ongoing, according to the release.

One person from the one-story home that exploded and five others, including three children, from one of the damaged homes next door were taken to hospitals for treatment, fire officials said. A person who was in the other damaged home wasn’t hurt.

The three adults were taken to Medical City Plano, where they remained hospitalized Wednesday. The hospital said one was in critical condition and two were in good condition.

A friend of the family next door who were injured said that the three children had been released from the hospital and were staying with family.

“From chatting with both parents, there was no flash, there were two explosions, and so the first one caught their attention, and then as the husband was facing the window, the second one went off, and that half of their house had collapsed in on them,” Mae Reedy told KXAS-TV.