The tragic incident unfolded Tuesday afternoon when two deputies on routine patrol saw Lopez carrying what they thought was a dangerous rifle, Santa Rosa police said.
The deputies drove up behind the boy, stopped their car and ordered him to drop the weapon, Santa Rosa police said.
The veteran deputy told investigators that Lopez began turning toward him and raised the gun's barrel in his direction, Henry said.
The senior deputy mistook the BB gun for an authentic assault rifle and opened fire, Henry said. The shots were fired within 10 seconds of the deputies' first report of a suspicious person, according to a timeline released by Santa Rosa police.
The deputy who shot Lopez is a 24-year veteran of the force who works as training officer, Assistant Sheriff Lorenzo Due?s said Thursday.
His partner, who did not fire his weapon, had been recently hired by the Sheriff's Office with 11 years of experience in law enforcement, Due?s said. He was undergoing training at the time of the incident.
Due?s declined to release the deputies' names. The Sheriff's Office and Santa Rosa police are investigating a series of death threats made against the two deputies.
"We have to protect our staff and make sure those threats aren't viable," Due?s said.
Due?s said the Sheriff's Office is aware that Lopez's death has evoked great emotions in the community. The agency is trying to balance its obligation to ensure staff safety against the public's right to know the identities of the deputies, he said. That process is expected to take at least two days, he said, possibly more.
"We're getting a lot of different messages with a lot of anger and we're trying to wade through what are threats and what is anger," Due?s said.
The Lopez family has apparently obtained an attorney from the Bay Area, but the family declined to speak to a reporter Thursday afternoon and would not reveal the name of their lawyer.
The family's call for "justice" has spread quickly through the local Latino community and beyond.
During the march Thursday evening, the demonstrators called out, "We want justice" and "Justice for Andy." There were also expletives directed at the police and sheriff's office.
Maria Lopez of Larkfield was at the Dollar Tree on Sebastopol Road getting balloons for a birthday party when she came across the protest. She is not related to the Lopez family.
Lopez, a house cleaner who came to the United States from central Mexico 35 years ago and became a U.S. citizen 16 years ago, said she had heard about the shooting and began to cry when she saw all the protestors.
"We're here to support the family. We're all supporting each other so that this won't happen again, so that they treat us like human beings," she said.
Many carried white balloons, scrawled with "RIP Andy Lopez," to honor the former Cook Middle School student.
"We're here to, like, show respect for Andy," said Adrian Leon, 12, a Cook student.
The march ended at Moorland and West Robles avenues, the site of the shooting. During another rosary reading, people released their white balloons into the air.
During Thursday's autopsy, Dr. Arthur Josselson with the Forensic Medical Group determined one of the fatal bullets entered the right side of Lopez's chest and a second fatal wound was caused by a bullet that entered his right hip, Henry said.