Emergency teams rushed Tuesday night to another reported explosion in Austin — this one at a Goodwill store — but police and federal authorities said the blast wasn't related to recent bombings that have killed and injured people and caused panic across Texas' capital for weeks.

Even as they pored through surveillance video footage and collected evidence hoping to get closer to tracking down whoever is behind the series of blasts that have killed two people and seriously wounded four others, a Tuesday night scare caused them to respond to a Goodwill store in southern Austin. It turned out to be an unrelated explosion: Someone dropped off a device sometimes used in military training and it went off, injuring a worker.

Police said they don't believe it was the work of the bomber, or a copycat. They said such military items are occasionally donated to Goodwill instead of being properly disposed of.

Gary Davis, president and CEO of Goodwill Texas, said the device known as an artillery simulator detonated when an employee tried to handle it.

"In this town, if an incendiary device goes off, everybody just scatters and panics," Davis said as he stood outside a police barrier huddling with other employees. "We're all on edge."

Even before the report of Tuesday night's explosion, it had already been a busy day. Before dawn, a bomb inside a package exploded around 1 a.m. as it passed along a conveyer belt at a FedEx shipping center near San Antonio, causing minor injuries to a worker. The Austin Police Department, the FBI and other federal agencies confirmed that the package center blast was related to four previous ones that killed two people and seriously injured four others.

That explosion occurred at a FedEx facility in Schertz, northeast of San Antonio and about 60 miles (95 kilometers) southwest of Austin.

Later in the morning, police sent a bomb squad to a FedEx facility outside the Austin airport to check on a suspicious package that was reported. Federal agencies and police later said that package had indeed contained an explosive that was successfully intercepted and that it, too, was tied to the other bombings.

Authorities also closed off an Austin-area FedEx store where they believe the bomb that exploded was shipped to the distribution center. They roped off a large area around the shopping center in the enclave of Sunset Valley and were collecting evidence, including surveillance camera footage.

U.S. Rep. Michael McCaul, a Republican from Austin who is chairman of the House Homeland Security Committee, said that investigators have obtained surveillance videos that "could possibly" show a suspect, but are still poring through video.

"I hope his biggest mistake was going through FedEx," McCaul, who has spoken to federal investigators and Austin police Chief Brian Manley, said of the bomber in a phone interview.

He added that the person responsible for the bombings had previously been "very sophisticated in going around surveillance cameras."

"They've got a couple of videos that could possibly be the person but they're not sure at this point," McCaul said.

Before it exploded, the package had been sent from Austin and was addressed to a home in Austin, Texas Attorney General Ken Paxton said.

In a statement, FedEx officials said the same person responsible for sending the package also shipped a second parcel that has been secured and turned over to law enforcement. A company spokeswoman refused to say if that second package might have been linked to the one reported at the distribution center near the airport.

The Schertz blast came less than two days after a bombing wounded two men Sunday night in a quiet Austin neighborhood about 3 miles (5 kilometers) from the FedEx store. It was triggered by a nearly invisible tripwire, suggesting a "higher level of sophistication" than agents saw in three package bombs previously left on doorsteps, according to Fred Milanowski, the agent in charge of the Houston division of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

A criminologist at the University of Alabama said if a single perpetrator is behind the blasts, changing the means of delivery increases the bomber's chance of getting caught.

"I think it would suggest that the bomber is trying to stay unpredictable," Adam Lankford said. "But it also increases the likelihood that he would make a mistake."

Authorities have not identified the two men who were hurt Sunday, saying only that they are in their 20s and white. But William Grote told The Associated Press that his grandson was one of them and that he had what appeared to be nails embedded in his knees.

In Washington, President Donald Trump said the assailant behind the bombing is "very sick."

During an Oval Office meeting Tuesday with Saudi Arabia's Crown Prince Mohammed bin Salman, the president said, "This is obviously a very sick individual or individuals," and authorities are "working to get to the bottom of it."

Despite bombing tactics that have now shifted, investigators have repeated prior warnings about not touching unexpected packages and urged people to be wary of any stray object left in public. Austin police say they have now responded to more than 1,200 reports of suspicious packages in a little more than a week — without finding anything dangerous.