AUSTIN—An apparent accident at a Goodwill store was briefly believed to be the work of the city’s serial bomber.

Over the past two weeks, five bombs in packages have exploded across the Texas capital, killing two people and injuring two others. A sixth bomb addressed to a location in Austin detonated at a FedEx facility outside San Antonio early Tuesday morning.

Then on Tuesday evening, a man was injured handling what police described as “artillery shell simulator” donated to the store.

“This was not an explosive device. This was an old, military-type ordnance,” an Austin police official told reporters. “There’s no reason to believe it is related to any other incidents that occurred.”

Texas Attorney General Ken Paxton told Fox News before the press conference that “the people on the ground that I’m talking to... they really believe this is the same bomber.” Paxton quickly backtracked in a subsequent interview with an Austin television station.

The response was all the same, though: Dozens of police vehicles with flashing lights sealed off the large strip mall. A convoy of armored vehicles and buses carrying ATF and FBI personnel came with sirens blaring.

Waiting to speak to federal agents outside the police cordon were Bryan and Maggie Landwermeyer, who own a building behind Goodwill.

They said they had set up a security camera to catch people using their Dumpster and plugging RVs into their power outlet. As soon as they heard about the explosion, the Landwermeyers said they contacted the ATF. Just before 9 p.m., a state trooper lifted the cordon and brought them in to be interviewed by the federal agents.

The stores are inside a large strip mall in a quiet suburban neighborhood.

“The worst crime we usually get is underage people trying to buy alcohol and cigarettes,” said Jerardo Jiminez, a clerk at the gas station across the street from Goodwill.