LOS ANGELES (CBSLA.com/AP) — A husband and wife from Taiwan found stabbed to death in their Diamond Bar home in October were probably robbery victims, Los Angeles County sheriff’s officials said Wednesday.

Cheng Long Wang, 60, and his wife, Mei Chu Chung, 57, were found slain on Oct. 20, 2016 after family members could not reach the couple, who immigrated to the U.S. in 2000.

“This couple was married for 30 years and were a classic example of the American success story,” Los Angeles County Sheriff Jim McDonnell told reporters.

Investigators suspect the couple had been victims of a robbery and about $15,000 had been taken from the home, said Los Angeles County Sheriff’s Capt. Steve Katz.

Officials would not say whether they believed the couple was targeted, but investigators believe the assailant knew the couple kept large amounts of cash in the home, Katz said.

The slaying was “extremely unusual” for the Southern California community and appears to have been an isolated incident, Katz said.

Cheng Long Wang worked as a computer programmer and Mei Chu Chung had taught art to children and offered lessons in a studio she had in their home, the couple’s adult son said. Both were very active in their community, he said.

The friend who came to check on the couple at the request of family members found Wang gravely injured, with multiple stab wounds, authorities said. Chung was also found mortally wounded with stab wounds and declared dead at the scene.

“They didn’t deserve a death like this,” said their son, Dr. Gary Wang, who flew in from Iowa to attend a news conference Wednesday. “They were just honest people who lived within their means.”

Wang said the loss of his parents has been difficult for him and his sister, but especially for his 4-year-old daughter, who used to video chat regularly with grandma and has cried at night for her grandparents.

On Wednesday, Los Angeles County Sheriff Jim McDonnell and County Supervisor Janice Hahn announced a $30,000 reward for information leading to an arrest and conviction in the case — $20,000 from the county Board of Supervisors announced in February and another $10,000 from the city of Diamond Bar.

Anyone with information about the case can call the Los Angeles County Sheriff’s Department homicide bureau at (323) 890-5500.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)