The boy's mother, Sujey Annel Cruz Cazarez, was grief-stricken in the living room.
"Why did they kill him? Why?" she said.
At 3 p.m., two sheriff's deputies patrolling in the area of Moorland and West Robles avenues observed Lopez walking with what sheriff's officials said appeared to be some type of rifle.
The deputies called for backup and repeatedly ordered the boy to drop the rifle, Sheriff's Lt. Dennis O'Leary said in a news release.
At some point after the deputies told Lopez to drop the rifle, they fired several rounds from their handguns at the boy, who was hit multiple times, O'Leary said.
After telling Lopez to move away from the rifle, deputies approached the unresponsive teen as he lay on the ground and handcuffed him before administering first aid and calling for medical assistance, O'Leary said.
Lopez was later pronounced dead at the scene. Neither deputy was injured, said Sheriff's Lt. Steve Brown. Sheriff's officials did not release the names of the deputies Tuesday, but said both had been placed on administrative leave.
After securing the scene, deputies discovered the rifle the teen was carrying was a replica of an assault weapon, O'Leary said. Deputies also found a plastic handgun in the teen's waistband.
The shooting took place at the edge of a field. The area was cordoned off for hours with yellow police tape. An ambulance and numerous patrol cars from both the Santa Rosa Police Department and Sheriff's Office surrounded the area.
Moorland Avenue was initially closed from West Robles to Corby avenues.