An autopsy will be performed, but Zweigart's death Saturday is believed to be from natural causes, said Jason Hanson, a Department of Corrections spokesman.
The death leaves 34 men and one woman on Oregon's death row. No inmate has been executed since 1997 and it might be years before another lethal injection occurs.
Gov. John Kitzhaber announced a moratorium on executions in 2011. One inmate, Gary Haugen, unsuccessfully pressed the courts to overrule Kitzhaber and order the state to kill him.
Zweigart, 64, died nine years to the day after entering death row. The meat cutter was convicted in the death of his wife, Hong Ha Zweigart, whom he met during his military service in Vietnam.
According to court records, Zweigart was working at supermarket in St. Helens -- 30 miles northwest of Portland -- when he began an extramarital affair with a co-worker. He hired the woman's nephew, 19-year-old Nicholas Fortier, to stage an armed robbery in his home and kill Hong Ha Zweigart in the process.
Zweigart put guns in the garage and left the door partially open to provide the teenager with easy access.
Twice, Fortier entered the garage but failed to follow through on the plan. On Jan. 10, 2002, Fortier made it into the couple's bedroom and pretended to be an armed robber. After ordering the couple downstairs and to lie on the floor, Fortier couldn't pull the trigger.
Zweigart, after urging Fortier to "do it," grabbed a gun, shot his wife and then handed the weapon to Fortier.
"He took the stand and denied doing it," Columbia County District Attorney R. Stephen Atchison recalled Monday. "He said it was a robbery and he was a victim like everybody else. The jury just chose not to believe that, based on the other things we had."
While awaiting trial, Zweigart solicited a cellmate to murder three prosecution witnesses, including two of his children and a supermarket co-worker.
The cellmate told sheriff's deputies, and Zweigart was tried and convicted.
More Northwest Headlines
Spokane man, 2 young children dead after crash in Idaho Longview woman indicted on federal child pornography charges Dig in Redmond uncovers 10,000-year-old stone tools Portland opens unique bike, pedestrian friendly bridge Seattle police say bystanders help catch sex offender September 26 a ‘free day’ at Washington State Parks JBLM soldier who disappeared during parachute exercise found dead Police: Oregon man urinated on passengers aboard JetBlue flight
Our new comment system is not supported in IE 7. Please upgrade your browser here.