Initially, investigators theorized that a bomb thrown from a passing car had caused the explosion at the 16th Street Baptist church. But by September 20, the FBI was able to confirm that the explosion had been caused by a device that was purposely planted beneath the steps to the church, close to the women's lounge. A section of wire and remnants of red plastic were discovered here, which could have been part of a timing device. (The plastic remnants were later lost by investigators.)