And unlike the victims of the previous blasts, the two men injured in Sunday’s explosion are white, Austin police said. Both men are expected to recover.

Latest developments

• The Travis Country neighborhood of Austin will remain on lockdown until 2 p.m. CT, Manley said, as authorities investigate the pieces of evidence strewn across a wide area.
• Manley asked anyone in the neighborhood with security camera footage to call police.
• The Austin public school district says it couldn’t send buses to the affected neighborhood Monday because of police activity.
• “As the bombmaker changes up design and geography, all residents of Austin and surrounding areas should avoid suspicious items,” the global think tank Stratfor Threat Lenssaid.

An indiscriminate wake-up call

Many minority residents in Austin have been on edge since the bombings started, as the first three bombings killed or wounded minorities.

Several residents under lockdown Monday said they were stunned the latest attack happened in their neighborhood.

Unlike the first three bombings, which happened in east Austin, the latest attack happened in a predominately white part of town.

Eliza May said because the first three bombings happening on the east side of the city, in predominately minority areas, she hadn’t been following the news closely.

May said as a resident of the affluent Travis Country neighborhood, she assumed she had nothing to worry about.

“We feel safe. This isn’t something that you’d expect around here,” May told CNN.

Now, “it’s obvious that you have to be alert.”

“This was a random bomb,” she said. “This could have been any one of us.”

Neighbor Shonda Mace said the bombing “is going to be life-changing event for our neighborhood.”

“I’m scared about what’s going to happen next,” she said.

Tripwire could give clues

“The use of a tripwire is far less discriminating than leaving parcel bombs at residences and suggests that the latest victims were not specifically targeted,” Stratfor Threat Lens said.

“The device’s success, despite significantly different design, further suggests that the bombmaker behind these attacks is an accomplished one, and has likely to have received some training, perhaps as a military or police explosive ordnance disposal technician.”

‘Extra level of vigilance’ needed

The latest blast came less than a week after police said the three previous explosions — in a span of 10 days — were connected. Those blasts killed a man and a teenager, and injured two others.

Police are working under the belief that the explosions are related. Manley said they’ll get a better idea with a post-blast analysis and examination of the device components.

In the meantime, Manley told residents not to touch or go near anything that looks suspicious.

“We now need the community to have an extra level of vigilance and pay attention to any suspicious device — whether it be a package or a bag, a backpack — anything that looks out of place,” Manley said Monday. “Do not approach items like that.”

Shortly before the fourth bombing, the reward for information leading to the arrest of anyone responsible for the three blasts increased to a total of $115,000, authorities said.

Officials have urged residents to call police with any tips they may have, even if the information seems to be “inconsequential.”