"None of them reported anything personally suggesting that any of them are at risk," ATF agent Stuart Lowery told reporters at a news conference in West Memphis Thursday afternoon.
Pierce is chairman of the board that has the power to revoke licenses of physicians and health-care professionals. More than 40 investigators from state and federal agencies are exploring leads, including the possibility that the bomber was someone with a grudge against the board.
Lowery and West Memphis police chief Bob Paudert appealed to the public for help in solving the bombing Wednesday morning outside Pierce's home in West Memphis. They would neither confirm nor deny reports that the bomb was under Pierce's car and was triggered when he moved a spare tire placed in front of the Lexus SUV.
"I dont want to comment on the complexity or placement of the device," Lowery said, adding that homemade bombs are limited "only by the imagination" of the builder, but all of them are designed to kill someone. The ATF says there are some 3,000 bombings each year in the United States.
Pierce lost an eye in the explosion and has numerous other wounds. Paudert said he is sedated but able to respond to his wife's voice when she whispers in his ear. He is in the critical care unit at The Med.
Authorities have put extra security around The Med and Crittenden Regional Hospital in case other doctors are at risk. Pierce is a family physician who worked at an office that is not part of the hospital.