A sixth package with an unexploded bomb was found Tuesday at a FedEx facility in Austin, Texas, hours after a package bound for the city exploded in a FedEx facility near San Antonio, injuring one, ABC News reports.

The Tuesday blast was the fifth since March 2, and the recent string of bombings has left the city on edge. Two people have died and another four injured as a result.

The package was believed to have been sent from a FedEx location in Sunset Valley, an enclave city within Austin, and was discovered by FedEx workers, the company said in a statement. Police have cordoned off the FedEx storefront there, and have described the unknown attacker as a “serial bomber.”

“We have also confirmed that the individual responsible [for Tuesday’s package bomb] also shipped a second package that has now been secured and turned over to law enforcement,” FedEx said.

The first three devices were hidden in packages hand-delivered to homes in residential neighborhoods. The fourth, which detonated Monday, was left on the side of the road and was rigged with a tripwire.

“What we have seen now is a significant change from what appeared to be three very-targeted attacks to what was, last night, an attack that would have hit a random victim that happened to walk by,” Brian Manley, the interim Austin police chief, said Monday, according to The Washington Post.

“So, we’ve definitely seen a change in the method.”