An FBI official on Monday pleaded with whoever is responsible for a series of bombings in Austin, Texas, to come forward.

“We would like him to reach out and talk to us,” said Christopher Combs, special agent in charge of the FBI’s San Antonio division.

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Austin Police Chief Brian Manley at the same press conference said officials see a "change in the method" employed by the suspect in last night's bombing compared to three previous bombings earlier this month.

"And 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," Manley said.

“So we’ve definitely seen a change in the method that this suspect or suspects is using,” Manley said.

Manley said authorities are working to determine if the incidents amount to domestic terrorism, but officials believe they are looking for "a serial bomber."

The Sunday night explosion, which left two people wounded, appears to have been ignited using a trip wire, officials said.

“This device is a little more sophisticated than what we have seen,” said Fred Milanowski, the special agent in charge of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) Houston division.

The ATF and the FBI are leading a “post-blast” probe, according to Manley.

“We have seen similarities in the device that exploded here last night and the other three devices that have exploded in Austin starting on March 2,” he said.

“Again this is preliminary information, but we have seen similarities.”

There is a $100,000 award for any tips leading to a suspect or suspects, in addition to a $115,000 award from the Texas governor’s office for the same information.

Two people were killed earlier this month from three package explosions in three different Austin neighborhoods, according to Reuters.

Updated at 12:33 p.m.