Two Oakland police officers apparently mistook an electronic scale commonly used to weigh drugs for a handgun when they opened fire on the owner of a hair salon Monday night, killing him, police said Friday.

Derrick Jones, 37, of Oakland also had marijuana in a glass jar in his pocket when police shot him on the 5800 block of Trask Street in East Oakland, said Officer Jeff Thomason, a department spokesman.

The two officers, who had responded to a report of a domestic dispute, shot Jones numerous times in the chest when he reached for his waistband, a police spokesman said.

The officers thought Jones was reaching for a gun, police said, but none was found. The scale Jones was holding was silver-colored and measured 3 by 5 inches, Thomason said.

Police declined to identify the officers who fired their weapons. But sources identified them as Officers Eriberto Perez-Angeles, who has been with the department for three years and is a member of the SWAT team, and Omar Daza-Quiroz, who has four years on the force.

Jones was on parole after serving nearly five months in state prison last year for a gun conviction, records show. He had previous arrests for drug possession and domestic violence, police said.

Police officials had initially declined to specify what the object was, citing concern for how that would affect Jones' family.

But on Friday, Jones' sister Tonya Saheli, 34, of San Leandro blasted police for killing her brother and for withholding that information. If anything, she said, news that police had killed Jones "because he had a scale and some weed" was damaging not to her family but to the department.

"My brother is gone over the fact that he had weed," Saheli said. "And they said they didn't want to reveal what it was because it would be embarrassing to my family? Are you serious?"

Saheli said, "It just magnifies my sentiments on the fact that they should not be given a pass. The fact that it was an electronic scale, it just really hurts."

Police said Jones, who owned a hair salon on Bancroft Avenue, had been the subject of a 911 call by a woman who said he choked and beat her. But Saheli said the woman, with whom Jones had a previous relationship, had "cried wolf" and made a "bogus call."

Jones ran from police because he believed he would be unfairly blamed for an incident in which the woman damaged his hairstyling shop, Saheli said.

Police said it was too early to say whether the shooting was justified. The officers who killed Jones are on paid administrative leave pending investigations by police homicide and internal affairs investigators and the Alameda County district attorney's office. An internal review board will determine if the incident warranted deadly force.

Asked by reporters this week about the incident, Police Chief Anthony Batts said he was reserving judgment.

But Batts said, "I do want to focus on the fact that we need to better ourselves in dealing with people who are going into waistbands, going into clothing, going into different aspects. We want to make sure that we give officers the proper training to address these things."