Tennessee Bureau of Investigation Director Mark Gwyn told reporters Richard Parker, 49, was taken into custody at his home and charged with two counts of felony first-degree murder and two counts of premeditated murder, the Tennessean reported. He also is charged with a single count of unlawful possession of an illegal weapon.
Parker was being held on $1 million bond in the Wilson County Jail, the Nashville newspaper said.
Parker, who has a previous conviction for arson in Giles County, is charged in the slayings of Jon Setzer, 74, a retired lawyer, and Marion Setzer, 72, of Lebanon, east of Nashville. The husband died in Monday's mail bombing and the wife succumbed to her injuries Wednesday, authorities said.
Authorities said a note had been recovered they believed was attached to the bomb. They declined to release its message.
Setzer picked up the package containing the bomb from a mailbox about 200 yards from the couple's home, officials said. It exploded as he returned to the house.
Authorities say they were investigating whether the package was delivered by a U.S. Postal Service carrier or a private delivery service.