Jose Valenzuela, 38, is accused of shooting Mike and Tina Careccia, then burying them in a 6-foot grave beside the home where he lived in Maricopa, Pinal County Sheriff Paul Babeu said Thursday.
The shooting stemmed from a disagreement after a Father's Day party where the friends had been celebrating together, Babeu said.
"Sometime later that evening, they went over to Valenzuela's home, and something happened, a fight ensued, and that's when he brandished a weapon," Babeu said.
Valenzuela "essentially confessed" to detectives Wednesday, the sheriff told reporters. He had the suspected weapon, a .22-caliber revolver, with him when he was taken into custody, Babeu said.
Authorities found the couple's bodies buried beside the house where Valenzuela lived with his family. The suspect told investigators he'd borrowed a backhoe from a friend and used it to dig the grave, Babeu said.
Investigators also have questioned a witness, Babeu said. So far, no other suspects have been charged, the sheriff said, but he added that the case is "evolving" as the investigation continues.
Couple on the way to work when they disappeared
Valenzuela told investigators he'd been friends with the couple for two years, and that they had used methamphetamine together, according to the sheriff.
He's being charged with two counts of first-degree murder and held on a $2 million cash bond, the sheriff said. A preliminary hearing in the case is set for July 10, according to jail records.
It was not immediately clear whether Valenzuela had retained legal representation.
Tina Careccia was on her way to work with her husband last month when they went missing
, relatives say.
Their dark gray 2008 Honda Accord was found abandoned.
"This is not just a search, but it is also criminal investigation into the couple's disappearance," Babeu said earlier this week.
Mike Careccia's son first reported the pair missing in a 911 call on June 22, telling a dispatcher his father, 44, and stepmother, 42, hadn't been seen all day after leaving home to head to work.
"I'm worried about him and ... their phones are off," he says in a recording released by authorities. "They've been gone for 12 hours now."