KVUE — Officials responded to an explosion possibly triggered by a tripwire in Southwest Austin Sunday night. They believe the incident might be connected to three other blasts around the city during the month of March, Austin police confirmed at a press conference.

The latest attack came hours after the Austin Police Department increased the reward offering for the three prior explosion investigations to $115,000.

Officials said on March 18 they responded to the 4800 block of Dawn Song Drive in Southwest Austin at 8:32 pm for an explosion. Two white men in their 20s were transported to South Austin Medical Center with serious injuries, according to Austin Interim Police Chief Brian Manley. At 11:30 pm, hospital staff confirmed to KVUE's Christy Millweard that the two men were in good condition. They're expected to be okay.

According to Chief Manley, it is possible Sunday's explosion was triggered by a tripwire as the victims either rode or walked their bikes along it.

An official told KVUE's Tony Plohetski that federal agents are convinced that a tripwire was used to trigger the explosion. The FBI is also looking into whether or not a copycat is responsible for the blast but added that investigators won't know for sure until the bomb materials and shrapnel are analyzed.

"That changes things in that our safety message to this point has been involving the handling of packages and telling communities, 'Do not handle packages. Do not pick up packages. Do not disturb packages,'" Manley said. "We now need the community to have an extra level of vigilance and pay attention to any suspicious device — whether it be a package, a bag, a backpack. Anything that looks out of place, do not approach it."

Police are asking anyone in the Travis Country neighborhood — about a half-mile radius — to wait in their homes until 10 am Monday and follow instructions from officers if and when given. Police said if a person in the immediate area has an emergency and needs to get outside of their home, they should call 911 first.

"We're asking you to stay in your residence until we've had the opportunity to ensure that this neighborhood is safe," Manley said.

Police said they are also working to clear a backpack found in the area.

They are asking anyone who sees a package to not even go near it and ask anyone who saw something suspicious to call 911 immediately

This last confirmed explosion follows three others in the month of March, two of which were deadly. The first was reported on March 2 in Northeast Austin in the Harris Ridge neighborhood. Anthony Stephan House, 39, an African-American man, was critically injured after finding a package on his front doorstep. He died the same day at the hospital.

The second explosion happened at a single-family home in Central East Austin on March 12. A 17-year-old African-American boy, identified as Draylen Mason, was killed and an African-American woman in her 40s was seriously injured.

A few hours after the explosion that killed the teen, a 75-year-old woman Hispanic woman, identified as Esperanza "Hope" Herrera, was injured in the third explosion in Southeast Austin after picking up a package left on her front doorstep. She remains in critical condition. During the media briefings for the first three explosions, police said they could not rule out the fact that the explosions might be a part of a hate crime. Police did not allude to the possibility of investigating a hate crime in the fourth explosion.

"We said from the beginning we weren't going to rule anything out because when you rule something out, you limit your focus," Manley said on Good Morning America March 19. "So this does change the concerns that we had initially. We have not ruled out [that this might be a part of a hate crime] until we understand the ideology or motive."

Police said the difference between the fourth explosion and the previous three is that it was not created by a suspicious package left on a doorstep. Manley said, in this case, this was a type of a suspicious package that was left on the side of the road that detonated and injured two men. He added that investigators will use lab results to determine if all four explosions are, in fact, related to the same suspect(s).

As police, the FBI and ATF investigate these possibly linked explosions, a $115,000 reward is being offered to anyone with information regarding the cases. To see how to submit a tip, go here.

Chief Manley said they need the public's help as they work to find a suspect.

"That's why we're pushing the message out that we need every tip, every piece of information," he said on GMA. "However inconsequential you think it is, that may be the one piece of evidence that we need."

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