Police said Friday that four of the five victims were members of the same family, but have not released further information on the relationships.
Ying Xue Lei, who also went by the name Jess Lei, worked as a software engineer at Quantitative Medical Systems in Emeryville, according to Roxanne Albertoli, an administrative assistant with the company.
"She was a wonderful person, she didn't deserve this," Albertoli said.
Albertoli said her co-workers knew something was wrong when Lei did not come in to work on Friday.
"She was a very fine worker, a very good engineer," Albertoli said.
Police on Sunday morning arrested Binh Thai Luc, 35, in connection with the killings.
The victims' manner of death is still under investigation by the medical examiner's office. Police Chief Greg Suhr initially said that some of the victims had been shot, but said at a news conference Sunday evening that further investigation revealed that was not the case.
Suhr said there was apparently an "edged" weapon involved, which he described as "a weapon capable of cutting you," but said no weapon has yet been recovered in connection with the deaths.
Suhr said Binh Thai Luc had some sort of relationship with the victims, but declined to comment on the nature of the relationship. He also said that Luc possibly had prior gang ties and has a criminal record.
Luc's brother, Brian Luc, 32, was also arrested on suspicion of narcotics possession, being a felon in possession of ammunition and a probation violation. The brothers live together in San Francisco, according to police.
Officers arrested the pair after serving search warrants at locations in San Francisco and San Mateo. Suhr said Binh Thai Luc was not arrested at his home.
The Police Department has until Tuesday to hand over the case to the district attorney's office, and the brothers could be arraigned as soon as Tuesday afternoon, district attorney's office spokeswoman Stephanie Ong Stillman said.
Police are continuing to investigate the murders. Anyone with information about the case is encouraged to call the department's homicide detail at (415) 553-1451, the anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.
*Note: An earlier version of this story misspelled victim Wan Yi Xu's name.