Wife Held in Death of Man’s Lover and Son : Crime: Li-Yun (Lisa) Peng was arrested on the basis of tests matching DNA from her blood with saliva lifted from a bite mark on victim’s arm.

A DNA sample from a bite mark on a dead body has led to a woman’s arrest on suspicion of murder in the deaths of her wealthy husband’s girlfriend and their infant son, the Orange County district attorney’s office said Monday.

Li-Yun (Lisa) Peng, 44, of Rancho Santa Margarita was arrested by Orange County sheriff’s deputies Saturday after criminologists had completed extensive tests of the suspect’s blood and a saliva sample taken from a bite wound on the arm of the victim, Jennifer Ji, 25, of Mission Viejo, said Ronald Cafferty, a deputy district attorney.

Ji was repeatedly stabbed. Her body was discovered by Tseng Jyi Peng, 50, Ji’s lover and the father of her 5-month-old son, Kevin, who had been suffocated in his crib. The bodies were found at the Vista Del Lago Apartments on Aug. 18.

Tseng Peng, a Rancho Santa Margarita resident, is chief executive officer of San Diego-based Ranger Communications, one of the world’s biggest manufacturers of citizens’ band radios with factories in Taiwan, Malaysia and China.

At first, Lisa Peng denied knowing about the deaths or that her husband had been having an affair with Ji, Cafferty said.

“When she was first interviewed by sheriff’s investigators, she told them she didn’t do it,” Cafferty said. “She also told investigators she didn’t know (her husband) had a girlfriend or had fathered a baby.”

An autopsy revealed that Ji, a 5-foot-7, 122-pound woman, died of 18 stab wounds, Cafferty said, adding that the woman’s son died after a blanket was stuffed into his mouth.

But it was a bite mark on Ji’s left arm that became the focus of the sheriff’s investigation. Cafferty said Sheriff’s Department criminologists swabbed the wound and retrieved saliva samples that matched Peng’s DNA taken from her blood.

DNA, or deoxyribonucleic acid, is the basic material of life and contains an individual’s genetic code. So-called genetic fingerprinting is used by prosecutors and investigators to link a suspect with a crime when witness testimony and other evidence are not strong enough.

At the time of the killings, sheriff’s deputies believed the killings were committed by someone the woman knew because there were no signs of forced entry to the two-bedroom apartment near Lake Mission Viejo.

After the grisly discoveries, deputies had interviewed both Peng and her husband. The couple had been in Taiwan just before the murders. Lisa Peng had returned to Orange County on Aug. 15, three days before the slayings, and her husband came back on the day Ji and the child died.

Peng’s husband called police after he found the victim’s bloody body sprawled on a living room couch about midnight.

Sheriff’s investigators initially had suspected both Pengs.

But Cafferty said the husband had an “iron-clad” alibi because he was in Taiwan at the time of the slayings.

Initially, witnesses at Ji’s apartment complex told investigators that they had heard noises coming from her apartment about midday. Lisa Peng told investigators that she could not have committed the murders because she was having lunch with one of her two children at the time.

Further investigation revealed that the killings were committed later, because Ji had called Peng in Taiwan in the afternoon, according to telephone records, Cafferty said.

Peng was arrested after she and her husband agreed to come in for further questions by investigators on Saturday. Both drove to the sheriff’s office, and after the interview she was taken into custody without incident, Cafferty said. She was being held in the Orange County Jail.

Peng’s arraignment is scheduled for today in Municipal Court in Laguna Niguel. Her husband could not be reached for comment Monday either at his office or home.

Prosecutors are expected to file murder charges and additional charges of special circumstances because it was a double homicide. If Peng is found guilty, the added charge could result in the death penalty.

“We will decide on whether to seek the death penalty at a later date,” Cafferty said. “I have a lot of things to look over, but if the penalty is justified, we will be adding it before the case gets to Superior Court.”

Times staff writer Len Hall contributed to this article.