“We have not had an opportunity to really look at this blast site to determine what has happened,” Chief Manley said at an evening news conference. “It’s obvious that there’s been an explosion, and it’s obvious it’s caused significant injuries to two people.”

At a news conference before Sunday’s explosion, the Austin police made a rare public appeal for the bomber or bombers responsible for the first three explosions to contact the police so officials could learn more about the “message” behind the attacks.

“These events in Austin have garnered worldwide attention, and we assure you that we are listening,” Chief Manley said in addressing the unknown bomber or bombers at the earlier news conference. “We want to understand what brought you to this point, and we want to listen to you.”

Chief Manley told reporters that he hoped the person or people responsible were watching, and that they would get in touch by calling 911 or reaching out online. He said investigators had not established a motive for the explosive packages.

“There’s the message behind what’s happening in our community, and we’re not going to understand that until the suspect or suspects reaches out to us to talk to us about what that message was,” Chief Manley said. “We still do not know what ideology may be behind this and what the motive was behind this.”