A Tennessee man was charged Thursday in the killing of his mother-in-law and father-in-law after a bomb exploded at their home this week, officials said.
Richard Parker, 49, was being held in lieu of $1-million bond after being arrested at his home Thursday, officials said.
A special Wilson County grand jury was convened and indicted him on charges of first-degree murder and premeditated murder in the Monday bombing.
Investigators said at a televised news conference Thursday that they thought Parker was solely responsible for the attack, but did not give specifics on what evidence led them to him.
Investigators did not cite a motive for the bombing. They said they were running tests on the explosive materials, which appear to have been planted rather than delivered by a mail or package service.
Authorities did not identify Parker's spouse. It was unclear how many children the Setzers had.
"Two people targeted for this kind of violence doesn't make sense at all," the Rev. Mike Ripski, senior pastor at First United Methodist Church in Lebanon, told the Tennessean newspaper before news broke of the arrest. The Setzers had attended Ripski's church.
"We are trying to make sense of this and so far we haven't been able to," Ripski told the newspaper. "If our faith is ever drawn on to sustain us through the unanswered questions, this is one of those occasions. The grief is deep, profound, because they were such wonderful people."
The bombing drew the attention of several federal agencies, including the FBI and U.S. Postal Inspection Service. Officials said Thursday there was an $8,000 reward for anyone who had information about the case.