The two got into an argument with the girlfriend and stole money from her purse and Masher's cell phone, the district attorney's office said.
Bilotti is accused of continuing the verbal altercation while Adams went into the kitchen for a knife. He allegedly punched Masher before stabbing him superficially. The two then fled the Newport Beach home.
Adams allegedly used Masher's stolen cell phone to text Masher's girlfriend to arrange to meet at Murdy Park, 7000 Norma Drive, Huntington Beach, to return the phone.
Bilotti drove Adams to the park, covering the license plate of her car first and hiding a folding knife in her vagina, according to the district attorney's office.
She waited in the car as Adams, with a handgun, waited for Masher's girlfriend, who arrived at 3:30 p.m. with Heintz and another friend.
Adams allegedly threw the phone at Heintz, shot him once in the stomach and headed back to the waiting car. Bilotti is accused of removing the license plate cover before driving off.
Witnesses called 911 and wrote down the license place number.
Heintz was treated at the scene by Fire Department paramedics, but was declared dead at a local hospital, said Lt. Mike Reynolds.
The Huntington Beach police caught up with Bilotti and Adams and found a handgun in their car, Reynolds said.
Bilotti was also charged with first-degree residential burglary and robbery, and Adams was also charged with first-degree robbery and aggravated assault with a sentencing enhancement for the personal discharge of a firearm causing death.
Bilotti is scheduled to be arraigned Nov. 19. Adams pleaded not guilty Tuesday and is due back in court next month.
Adams faces a maximum sentence of 57 years to life in prison and Bilotti faces 31 years to life in prison if convicted on all charges. Both are being held on $1-million bail.