PFLUGERVILLE, Texas — Investigators on Thursday finished questioning the second roommate of the man they say spent weeks planting bombs around Texas’ capital before using one of his own devices to blow himself up, but a more complete picture of the 23-year-old community college dropout remains elusive.

Police said they’d released the second of two people who shared a home in Pflugerville, just north of Austin, with serial bombing suspect Mark Conditt. The other roommate was taken into custody Wednesday and released hours later. Investigators haven’t named them, saying they weren’t under arrest.

Conditt made a 25-minute cellphone recording before his death. It was recovered Wednesday, after he detonated one of his own bombs along the side of Interstate 35 just outside of Austin as a SWAT team moved in. But investigators say the recording provides few clues as to Conditt’s motives – and they’ve refused to release it publicly, citing the ongoing investigation.

Conditt built bombs planted in different parts of the city that killed two people and severely wounded four others over three weeks starting on March 2. He began by placing explosives in packages left overnight on doorsteps, then rigged an explosive to a tripwire along a public trail. Finally, he sent two parcels with bombs via FedEx.

All of the early victims were black or Hispanic, though the tripwire bomb injured two white men. As fear grew, Conditt eventually was tracked down through store surveillance video, cellphone signals and witness accounts of a customer shipping FedEx packages in a disguise that included a blond wig and gloves.

Police found him early Wednesday at a hotel. And when his car moved, they followed and forced him off the road, setting up the confrontation that ended in an explosion.