Eric Williams was locked up overnight on a charge of making a terrorist threat and held on $3 million bond, The Dallas Morning News reported.
He was not charged with killing Mike McLelland, 63, and his wife, Cynthia, 65, in their home near Forney, Texas, March 30, or with the Jan. 31 shooting death of Assistant District Attorney Mark Hasse, 57, outside the Kaufman County Court House.
Williams has denied any role in the slayings and was cooperating in the investigation, CBS News said.
Details of the alleged terrorist threat were not immediately revealed.
Williams, 46, was convicted last year of stealing equipment that belonged to the county. The conviction cost Williams his license to practice law and apparently put him on the list of potential suspects with a grudge against the DA's office.
There had been speculation Mike and Cynthia McLelland and Mark Haase may have been the victims white supremacist prison gang members.