LATEST: Police reopen streets roughly 24 hours after Sunday night bombing in Southwest Austin

9 p.m. update: Police are reopening the scene where a bombing happened Sunday night.

A patch of lawn near a sidewalk on Dawn Song Drive had visible damage Monday night. It appears to be the site where authorities say an explosive device detonated Sunday night, injuring two men. The explosion was the fourth in a series of bombing attacks this month. Katie Hall / AMERICAN-STATESMAN

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Streets in the Southwest Austin neighborhood that police had previously shut down — including Eagle Feather Drive, Travis Country Circle, Republic of Texas Boulevard and Mission Oaks Boulevard — are either currently open or will be open soon, police said.

7 p.m. update: As investigators continue to seek the person or people responsible for bombings across the city, Austin school officials and police are now conducting perimeter checks for any suspicious items inside or outside of school buildings, Superintendent Paul Cruz wrote in an email to families on Monday.

Officials are also carefully examining all mail deliveries to school campuses, Cruz wrote.

“We remain vigilant with our safety and security measures, and we need your help,” Cruz wrote. “Talk with your students about being cautious. Make sure they understand they should not touch anything unusual or suspicious and should report it to a trusted adult or the police. Remind other adults, your friends, family and neighbors to do the same. No matter how minor, if you see something, it needs to be reported to ... 911.”

Several people suggested at a recent town hall forum last week that schools should reach out to parents to spread the news of the mail bombings.

3:30 p.m. update: The two victims in Sunday night's bombing were Will Grote and Colton Mathis, according to Julia Thompson, who went to high school with both men and is a family friend of the Grotes.

Both victims, who are in their mid-20s, are in “good condition” at St. David’s South Austin Medical Center, a hospital spokeswoman said.

Thompson, 21, who grew up in the neighborhood, was babysitting two young boys at another family friend’s house on the block when the explosion occurred Sunday evening. She didn’t hear the explosion but heard the rush of sirens that followed.

Thompson said she has been interviewed by the FBI several times. She wasn’t able to leave the house until Monday afternoon because investigators were searching the area for additional explosives.

“We’ve been locked inside all day,” said Thompson, whose father and uncle have been in communication with Grote’s father since Sunday night.

Police are now letting people back onto streets at the scene — Eagle Feather Drive and Travis Country Circle — on a limited basis.

Residents can enter from Southwest Parkway at Republic of Texas Boulevard. But Republic of Texas Boulevard is closed beyond Travis Country Circle, and Mission Oaks Boulevard remains closed.

2:30 p.m. update: Texas Gov. Greg Abbott said Monday his office will give investigators the money to buy seven portable x-ray systems to look inside suspicious packages in Austin.

Investigators are already using some x-ray systems for bomb detection as they respond to suspicious package calls, state officials said. A vendor has already loaned two x-ray systems to Austin police for this purpose, and the grant will allow them to buy these two in addition to two others.

The Texas Rangers can purchase three x-ray systems with this grant.

Austin police expressed a need for these x-ray systems.

Abbott’s office is providing $265,500 for these seven devices. Over the last two years, the governor’s office has provided about $1 million to Austin’s bomb squad to purchase robots and bomb suits, the office said.

10:25 a.m. update: Austin police are asking residents in Southwest Austin neighborhood to give investigators any surveillance footage from their homes after a bomb explosion injured two men in the area Sunday night.

Investigators work at the scene of a bombing on Dawn Song Drive in the Travis Country neighborhood on Monday.    JAY JANNER / AMERICAN-STATESMAN

Credit: Jay Janner

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Credit: Jay Janner

Interim Police Chief Brian Manley confirmed that investigators believe the bomb was similar to the other bombs that exploded in Austin this month, and was activated by a trip wire – a development that authorities say indicates a higher level of sophistication and more danger because a trip wire isn’t targeting a specific person.

Manley said residents can call Austin police at 512-974-5210 to turn over their video.

The Travis Country neighborhood would continue to be under lockdown until 2 p.m., the chief said, adding that police wanted to use “an overabundance of caution to process the scene.”

Debris had been strewn over some distance, Manley said, which made cataloging evidence a challenge in the dark.

Manley, flanked by federal authorities in a public briefing on Monday, said residents should not only avoid suspicious packages, bags or backpacks, but also avoid moving them because of the possibility of trip wires.

Authorities say trip wires can detonate a bomb whenever any pressure is put on the wire by wither tripping over it or pulling on it.

Call 911 if you see any suspicious packages, Manley said, adding that authorities will bring in extra bomb-detecting dogs.

In addition to personnel from San Antonio and Houston police, more than 500 federal officers, including 350 FBI agents, also are assisting Austin police in the investigation, authorities said.

Manley also provided additional details about the explosion Sunday night. He said two men, only identified as a 22-year-old and 23-year-old “Anglo males,” were walking along the side of the road when the blast occurred around 8:30 p.m.

The men were hospitalized with “significant injuries,” the chief said.

As of Monday afternoon, both men remained in good condition at St. David’s South Austin Medical Center, a hospital spokesperson said.

8 a.m. update: If police confirm that Sunday night's bomb in Southwest Austin was triggered by a trip wire, the device would be "showing a different level of skill above what we were already concerned that this suspect or suspects may possess," interim Police Chief Brian Manley said Monday.

A bicycle remains in the middle of the street on Dawn Song Drive in the Travis Country neighborhood on Monday, the morning after a bomb exploded.  JAY JANNER / AMERICAN-STATESMAN

Credit: Jay Janner

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Credit: Jay Janner

In an interview with David Muir on ABC’s “Good Morning America,” Manley urged the public to provide any tip, “however inconsequential you think it is, that may be the one piece of evidence that we need.”

Investigators are more certain Monday morning that the explosive device that detonated in Southwest Austin was activated by a trip wire made to blend in with surroundings, a law enforcement official told the American-Statesman.

They are investigating whether the blast, which injured two men, was the result of a copy cat or the same person responsible for three previous explosions that killed two people and seriously wounded a 75-year-old woman. That determination likely won’t be made until officials can more closely review the kind of shrapnel that was used in the explosive device.

Officials think that the trip wire was activated by pedestrians or someone on a bicycle, the official said.

In the television interview Monday, Manley also addressed speculation that the bombings, which killed two African-Americans in neighborhoods east of Interstate 35, could be a hate crime.

“The victims in this incident were two Anglo males,” the chief said. “We’ve said from the beginning that were not willing to rule anything out, just because when you rule something out you limit your focus.”

He said police are still trying to understand what the ideology or motive is behind the bombings.

Manley also said that “at this point, we have people we have looked at, but there’s no leading suspect at this time.”

Earlier: Police on Monday are telling residents in a Southwest Austin neighborhood to stay in place until 10 a.m., as officers continue to investigate a bomb that exploded Sunday night.

“If you are receiving an emergency alert to stay in place, this only applies to residents that live in the Travis Country neighborhood,” police said via Twitter on Monday morning.

The Travis Country neighborhood extends from Southwest Parkway north to the Barton Creek Greenbelt and includes homes on Dawn Song and Eagle Feather drives near Republic of Texas Boulevard, where the explosion happened.

However, residents as far as away as Del Valle said they were receiving the warnings to stay inside and to call 911 if they needed to leave before 10 a.m.

Austin police say the warning is intended only for those in the Travis Country neighborhood.

“The scene needs to be processed and properly cleared of any hazards,” police said. “Updates will be provided to residents around 10 a.m.”

Two men were injured and sent to the hospital after an explosion on Dawn Song Drive just north of Southwest Parkway near the MoPac interchange. The bombing was the third in less than a week and the fourth this month.

The first three bombs were left as packages on doorsteps at three homes. The first blast on March 2 killed 39-year-old Anthony Stephan House in Northeast Austin. Ten days later, two more bombs exploded. One package killed 17-year-old Draylen Mason and injured his mother in their East Austin home; the other package exploded and injured 75-year-old Esperanza Herrera in Southeast Austin.

Police are not ruling out the possibility that the explosion Sunday night in Southwest Austin was triggered by a tripwire, interim Police Chief Brian Manley said early Monday, signaling a departure in the type of explosive device used.

He warned residents to be even more vigilant.

“That changes things,” Manley added. “Our safety message to this point has been involving the handling of packages, and telling this community ‘Do not handle packages, do not pick up packages, do not disturb packages.’ We now need 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 and please do not approach it.”

American-Statesman reporter Brandon Mulder contributed to this article.