A preliminary autopsy report released Thursday said Andy Lopez was shot seven times, and the two fatal wounds were in his right hip and the right side of his chest.
The final autopsy results won't be ready for several weeks.
Meanwhile, hundreds of people marched more than 3 miles from Santa Rosa City Hall to the field where Andy Lopez was killed Tuesday afternoon. Some lit candles and placed flowers at a makeshift memorial with printed pictures of the victim, stuffed animals and a balloon that read "RIP Andy L." An Aztec dance performance followed the march.
"It's very tragic and sad. It just happened so quick," said Noel Nunez, 15, a sophomore at nearby Elsie Allen High School. Still, he said deputies should have been able to tell the difference between a real gun and a replica weapon.
A Sonoma County sheriff's deputy twice told the boy to drop the weapon, but he instead raised it in the deputy's direction, police said at a news conference Wednesday.
"The deputy's mindset was that he was fearful that he was going to be shot," said Santa Rosa police Lt. Paul Henry, whose agency is investigating the shooting in the suburban town of roughly 170,000 people. It's about 50 miles northwest of San Francisco in California's wine country.
The gun looked just like an AK-47 assault rifle, with a black body and ammunition magazine, and a brown butt and grip. Only after the shooting did deputies realize it was a plastic replica, authorities said.
"Nobody should die for a misunderstanding, especially not a young boy who hasn't even started his life. It's just really sad knowing that," said Viviany Diaz Agirra Torres, 17. Torres said she wanted to know whether police gave Andy time to put the gun down before opening fire.
Hundreds of community members marched Wednesday night to remember the teen and protest the shooting, chanting "We need justice," the Press Democrat of Santa Rosa reported.
Police said two deputies were riding in a marked patrol vehicle and were in uniforms when they spotted Andy in a hooded sweatshirt and shorts at 3:14 p.m. Tuesday. His back was turned toward the deputies, and they did not realize he was a boy.
One of the deputies saw what appeared to be an assault rifle similar to an AK-47 in the teen's left hand. The deputies pulled over and took cover behind one of the vehicle's doors, according to police.
A witness reported seeing the patrol car's overhead emergency lights turn on and hearing the chirp of a siren, police said.
One of the deputies twice ordered Andy to drop the weapon, according to a witness, police said.
The teen was about 20 or 30 feet away from the deputies with his back toward them when he began turning around with what one deputy described as the barrel of the rifle rising up and turning in his direction, police said.
One deputy then fired several rounds, striking the boy at least once, Henry said. He was pronounced dead at the scene.
Investigators said they believe eight rounds were fired. The timeline released by Santa Rosa police says those shots were fired within 10 seconds of the deputies' first report of a suspicious person.
At Wednesday's news conference, Santa Rosa police displayed the pellet gun alongside a real AK-47. The two appeared strikingly similar.
Deputies also found a plastic handgun in the boy's waistband, police said.
The pellet gun did not have an orange-tipped barrel like other replica firearms, including the plastic handgun found in the boy's waistband, police said.
The deputies, who have not been identified, have been placed on administrative leave, which is standard after a shooting, sheriff's officials said.
Assistant Sheriff Lorenzo Duenas told the Press Democrat that the deputy who shot the teen is a 24-year veteran and his partner, who did not fire his weapon, is a new hire.
Thanawala reported from San Francisco.