Phoenix police said Sunday that they may never learn exactly why a 56-year-old man fatally shot a family of four who lived next door before killing himself in a townhouse complex in Phoenix, reports azcentral.com .

But neighbors in the family-oriented, 250-unit complex, near 17th Avenue and Hazelwood Street, said the shooter often argued with pet owners about barking dogs and left written notes complaining about the noise.

“He didn’t want noise,” neighbor and dog owner Denise Lopez said. “The dogs were waking him up. He always used to complain.”

What is known, according to police, is that Michael Dante Guzzo took his pump-action shotgun and, at about 9a.m. Saturday, fatally shot his next-door neighbors: Bruce Moore, 66; his daughter, Renee, 36; her husband, Michael, 42, who took his wife’s last name; their son, Shannon, 17; and two dogs.