Peter Gomez, a 54-year-old carpenter who lives about 200 yards from the home, said he had seen the family — a husband and wife and their four children — pass by many times but didn’t know them personally.
“It’s a horrible thing,” Mr. Gomez said. “You see all this stuff that happens all over the country, the shootings in the schools and theaters, and then it happens right here. It’s sad.”
Authorities declined to release details of any conversation that the 15-year-old had with investigators, but they said he was the Griegos’ son.
The sheriff’s office said it wouldn’t release any further information about the case until Sheriff Dan Houston holds a news conference Tuesday morning.
The teen was expected to make his first court appearance Tuesday afternoon.
• Associated Press writer Paul Davenport in Phoenix contributed to this article.