Investigators say they believe there is a connection between three package bombings in Austin, Texas.
The first explosion happened in early March killing one black man.
The other two explosions happened within five hours of each other. One killed a teenage black boy and seriously injured an adult woman. The other detonated at a house farther south, seriously injuring a Hispanic elderly woman.
Interim Chief of Police Brian Manley told KXAN the packages were average size boxes.
"We will leave no stone unturned because we are not going to allow this to go on in our city," Manley said.
Investigators say it's too early to say what motivated the attacks but have not ruled out a hate crime.
The two victims killed in the explosions are relatives of prominent members of Austin's African American community, the Washington Post reports.
The first victim, 39-year-old Anthony Stephan House, was the stepson of Freddie Dixon, a former pastor at a historic black church in the city.
The second victim, who was 17-years-old, is the grandson of Norman Mason, a dentist in the area who mentored African American student-athletes at the University of Texas at Austin.
Mason's wife, Lavonne confirmed that her grandson was killed in the explosion Monday morning.
"Are you trying to say something to prominent African American families?" Freddie Dixon asked. "I don't know who they've been targeting, but for sure, they went and got one of my best friends' grandson. Somebody knew the connection."
The FBI and police are urging residents to be cautious about approaching packages left at their doorsteps unexpectedly.
There is a $15,000 reward for information about the explosions.