The trial lasted more than 3 weeks, but it took the jury less than eight hours to return with a guilty verdict on Thursday. The jury also found the allegation that she personally used the firearm to be true.
The 51-year-old showed no reaction when the verdict was read. Her husband left the courtroom immediately, and her mother left in tears about a minute later.
Lazarus' attorney already says he plans to appeal.
"I am very disappointed. I think the speed of the verdict showed that we never had a chance in this case," said defense attorney Mark Overland.
Sherri Rasmussen, a 29-year-old nurse, was found dead in her Van Nuys apartment in 1986. Sherri Rasmussen was a 29-year-old nurse who was found shot dead in her home. Her husband, John Rutten, had been romantically involved with Lazarus. The prosecution contended Lazarus murdered her ex-boyfriend's wife in a jealous rage.
The key piece of evidence in this case was DNA from a bite mark on the victim's arm. Investigators say that DNA came from Lazarus, who was an LAPD officer at the time. Lazarus went on to become a detective.
The case had originally gone cold, and detectives had believed at the time that the murder was the result of a burglary that had been interrupted. In 2004, detectives reopened the case after discovering the DNA evidence, but it wasn't until 2009 that the evidence brought investigators to Lazarus.
The defense argued that the DNA was improperly stored and could have been contaminated or planted, but the jury didn't buy it.
"Today's verdict absolutely confirms the identity of the person who murdered their daughter, and the intent with which she committed this crime," said John Taylor, the Rasmussen family attorney.
Rasmussen's family plans to file a lawsuit against the city, but they said they are very grateful for the current detectives who they say were dedicated to solving the murder.
"This case was a tragedy on every level," said LAPD Chief Charlie Beck in a statement. "Not only did the family of Sherri Rasmussen lose a wife and a daughter, a life that can never be returned, but also the LAPD family felt a sense of betrayal to have an officer commit such a terrible crime."
Lazarus faces 27 years to life in prison when she is sentenced on May 4.