A man who killed his son in 2008 to collect $700,000 from his life insurance policy was convicted this week of killing his wife nearly 30 years ago for the same reason.

The man, Karl Holger Karlsen, 59, pleaded guilty in 2013 to murdering his son, Levi Karlsen, in Seneca Falls, N.Y., and was sentenced to 15 years to life in prison. That conviction raised the suspicions with detectives in California, where the investigation into his wife’s death had been continuing, according to court documents.

Mr. Karlsen’s wife, Christina A. Karlsen, 30, died on New Year’s Day in 1991, when she was trapped by a fire in a boarded up bathroom of the family home in Calaveras County, Mr. Karlsen’s lawyer, Richard Esquivel, said.

Days after his wife’s death, Mr. Karlsen collected $215,000 from his wife’s insurance policy and he and his children moved to Seneca Falls, N.Y., where he is from, Mr. Esquivel said.