Fatal unsolved bombings in Texas this month were "meant to send a message," Austin Police Chief Brian Manley said Sunday during a news conference, but the message is unknown, NBC News reported.
Manley said he hoped the bomber would "reach out to us before anyone else is injured or killed."
The plea came while local and federal officials increased the reward for information leading to a conviction in the bombings, which killed two and injured two others this month. The reward is estimated at $100,000.
Austin police are investigating another explosion in the southwestern residential part of the city after two men sustained non-life-threatening injuries and were examining a suspicious backpack in the area.