Authorities released details Sunday from a weekend shooting attack that left four family members and two dogs dead at a central Phoenix townhouse before the gunman turned the weapon on himself.

Michael Guzzo, 56, killed his next door neighbors in a deadly confrontation Saturday that may have been touched off by loud barking, police said.

Phoenix police Sgt. Tommy Thompson said there is "some indication that perhaps that was a problem." But he added that because of the deaths, a motive may never be known.

The victims have been identified as Bruce Moore, 66; his daughter, Renee Moore, 36; her husband, who took his wife's name, Michael Moore, 42; and Renee's son, Shannon Moore, 17.

After the killings, Guzzo shot at another townhouse before returning to his unit and killing himself, police said.

Police said they found a pump shotgun, apparently the weapon used in the killings, next to his body. Thompson said there was no indication he had a violent past.

A neighbor said Guzzo usually kept to himself.

"I've seen him every morning _ come in quiet every morning," Donald McKenzie told Phoenix television station KSAZ-TV ( http://bit.ly/1a8DGFH). "Never would expect him to be the guy who did this at all."

Another neighbor, Barry Hatchett, told Phoenix station KNXV-TV ( http://bit.ly/19JezfR) that he was friends with Renee Moore. Hatchett said he had planned to take his dog to the Moore's home for a grooming appointment later Saturday.

After shooting the Moores and the dogs, Guzzo then walked across the large complex and shot at the door and second floor of another townhouse, police said.

KNXV-TV reports the second home belongs to Libni DeLeon, who said bullet holes are now scattered around his house.

DeLeon told the station he heard a knock Saturday morning before the gunman shot through his front door.

"I ran upstairs and when I got there I got a glance at him, and I yelled at him, and he turned around and shot two more rounds upstairs," DeLeon said.

No one was injured at the home.

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AP Writer Barry Massey contributed to this report.