The FBI said Tuesday that a package that exploded at a FedEx facility outside San Antonio, Texas, was likely linked to four recent explosions in Austin.
The bomb detonated just after midnight, injuring one employee who was treated at the scene. Police believe the package was headed to Austin, but did not release details about where exactly it was meant to go.
The incident strengthened law enforcement officials' suspicions, expressed Monday by Austin Police Chief Brian Manley, that "we are clearly dealing with what we expect to be a serial bomber at this point."
"We suspect it is related to our investigation," confirmed Michelle Lee, a spokesperson for the FBI's San Antonio office.
The string of explosions has perplexed officials, who initially suspected the crimes could be racially-motivated when the first three package bombs went off in East Austin, which has a large black and Latino population. Two people were killed and three were injured in the first three incidents.
The fourth explosion, on Sunday, happened in the predominantly white neighborhood of Travis Country, several miles from the previous bombings, and injured two people. The bomb was rigged with a tripwire, indicating "a higher level of sophistication," by the person or group behind that explosion, according to Manley.
"We don't know why the bomber is doing this, we don't know his reasons," Christopher Combs, special agent in charge of the San Antonio FBI office, told the Texas Tribune after Tuesday's explosion.