During the July 28 incident, a carjacking suspect crashed a stolen car, fired at deputies and fled into a neighborhood. A search ensued, and that suspect was taken into custody.
Around the same time, a resident in the neighborhood noticed 27-year-old Donnell Thompson lying in his yard and called 911. Sheriff's officials said deputies were concerned that Thompson may be armed and possibly connected to the carjacking suspect.
Deputies said Thompson did not respond to their attempts to communicate with him and was lying in a position that covered one of his hands from view. At one point, investigators said Thompson stood up and "charged at the deputies."
That's when a deputy fatally shot Thompson, believing he was armed. According to the sheriff's department, the deputy who shot Thompson fire from the turret of an armored vehicle.
After the shooting, authorities launched an investigation, which included gun residue testing, DNA testing, interviews with witnesses, deputies and family members and fingerprinting.
The sheriff's department released a statement Tuesday on its findings.
"We have determined that there is no evidence that Mr. Thompson was in the carjacked vehicle, nor that he was involved in the assault on the deputies," the statement said.
Dawn Modkins, a spokeswoman for Black Lives Matter Long Beach, organized a press conference with Thompson's family and friends in front of the Los Angeles County Board of Supervisors building after the information was released.
Thompson's family, who called him "Little Bo Peep," said they plan to file a wrongful-death lawsuit against the sheriff's department. His brother said Thompson was a "kind, sweet person" who did not have a criminal history.
His family and friends said they wanted justice for his death and that the sheriff's department needed to publicly apologize.
"We want the sheriff's department to be held accountable for their actions. We want an apology to us as his family (and) a public apology to the community for their reckless actions on July 28," Thompson's sister-in-law said.
Matrice Stanley, 44, one of Thompson's sisters, said she and the rest of her family did not learn about his death until several hours later that day.
"Justice is not going to bring my brother back," she said.
Stanley said her brother had a diminished mental capacity, was reserved, extremely quiet and non-confrontational. She said she believed her brother's race was a major factor in why he was shot.
"My brother was dehumanized, disvalued," Stanley said. "I wouldn't treat an animal this bad. How is this justifiable?"
Stanley also expressed anger about the deputy firing from an armored vehicle.
"He can't go through armored cars," she exclaimed.
The deputy involved in the shooting has been reassigned to non-field duties, authorities said.
The shooting was under investigation. It will ultimately be turned over to the county district attorney's office for review.
The Associated Press contributed to this report.