Two men in Austin were injured Sunday while riding or pushing their bicycles as packaged explosives detonated nearby.
It’s the fourth explosion to rock Austin since March 2.
Mayor Steve Adler told The Associated Press on Monday that the growing anxieties about suspicious package explosions are “legitimate and real” and that residents shouldn’t think twice about calling 911 if they see anything suspicious.
The bombings began March 2.
The first bombing occurred on March 2 on Austin’s Haverford Drive and killed Anthony Stephan House, a 39-year-old African-American man.
Draylen Mason, a 17-year-old African-American male, was killed in the second bombing on the morning of March 12. Mason’s 41-year-old mother was also critically injured in the same explosion.
A third explosion later that day severely injured Esperanza Herrera, a 75-year-old Hispanic woman who on Sunday was “still fighting for her life,” Manley said.
Manley told ABC’s "Good Morning America" on Monday that Sunday night’s explosion was detonated by a tripwire and showed "a different level of skill." The attack differed from the three earlier blasts in Austin this month, which were caused by package bombs left on people’s doorsteps.
As of Sunday, police have received 735 calls for suspicious packages, the Austin American-Statesman reported.
A bomb scare Saturday led to an arrest and the cancellation of a highly anticipated South by Southwest concert.
On Saturday night, a bomb scare led to the cancellation of the highly anticipated The Roots concert. Later that night, 26-year-old Trevor Weldon Ingram was arrested and charged with emailing the threat.
Ingram faces up to 10 years in prison on charges of making a terroristic threat, but police said they do not think he is connected to the earlier bombings.
Police still don’t know the motive behind the bombings.
According to the Austin American-Statesman, more than 500 agents from the FBI, police and Bureau of Alcohol Tobacco Firearms are involved in the investigation.
But despite the 435 leads and 236 interviews, police still don’t have a motive.
Because of the previous victims’ races, police haven’t yet ruled out the possibility of hate crimes. The men injured in Sunday’s blast, however, were white, unlike the victims of the first three bombings, who were black or Hispanic.
The first three explosions also detonated in the eastern part of Austin, areas with predominantly black and Hispanic residents.
“We are working under the belief that this is related to the other bombing incidents that have occurred in our community over the last couple weeks,” Manley said at a news conference Monday morning.
There’s a $115,000 reward for information leading to arrest.
Following the fourth bombing on Sunday, Austin police announced a $50,000 increase to the previous $50,000 reward offered in exchange for information leading to an arrest of the bomber behind the deadly explosions.
Texas Gov. Greg Abbott added an additional $15,000, bringing the total reward amount to $115,000.
“We’re hoping to encourage you to come forward with the addition of this tip money that’s now available,” Manley said. “The person or persons understand what that message is, and is responsible for constructing or delivering these devices, and we hope this person or persons is watching and will reach out to us before anyone else is injured or killed out of this even.”
Police are warning residents to continue to be cautious about suspicious packages.
Manley has advised Austin residents to be cautious about packages they weren’t expecting. “If you see something suspicious please dial 9-1-1,” Austin police tweeted last week.
Security officials at the University of Texas at Austin also urged students to report suspicious items. "When you get on campus this morning ASK your friends if they’ve heard about the bombings. TELL them about the incidents,” university police tweeted.
“We know that if these bombings would have happened on the west side, there would have only been one. They would have locked down the community and made sure it wouldn’t happen again,” Fatima Mann, the executive director of Counter Balance: ATX, an activist organization that works with low-income and minority groups in the city, told the Washington Post.
The city is divided by Interstate 35, which runs north through the heart of the state capital. The first three explosions this month have occurred on the east of I-35, home to black and Latino residents historically. Sunday night’s explosion happened on the other side, in the southwestern Austin residential neighborhood of Travis Country.
And according to the Washington Post, the Austin Police Department took days to inform the public that the March 2 package explosion killed 39-year-old Anthony Stephan House. His death was initially classified as a “suspicious death, not a homicide.”
“We can’t rule out that Mr. House didn’t construct this himself and accidentally detonate it, in which case it would be an accidental death,” Assistant Chief Joseph Chacon said at the time, a statement that brought criticism from Austin residents.
“I apologize the department put that out there because that was not appropriate,” Manley said in response to the outrage. “It may have been something that needed to have been evaluated, but it’s not something that needed to be said publicly.”
According to a series by the Austin American-Statesman, the Texas capital has some of the highest rates of income segregation in the nation.
The series also found that years of housing discrimination limiting African-Americans’ ability to own property in Austin still impacts the demographic today.
The Associated Press contributed to this story.