Three separate package bombs have gone off in Austin, Texas in the past two weeks, killing Stephen House, 39, and Draylen Mason,17. Mason’s mother and an elderly woman were also injured in the bombings.

Austin’s interim Police Chief Brian Manley told the media the packages were placed in front of the residents’ houses. According to Manley they appeared to be “average-sized delivery boxes, not exceptionally large.”

The first bomb detonated in northeast Austin on March 2 with a force strong enough to kill House and alarm his neighbors. The package exploded after House picked it up outside his home. At the time, authorities said the blast was “suspicious” but likely “an isolated incident” that posed no ongoing danger to the community.

On Monday, March 12 two packages left in other parts of the city also detonated; one killed Mason and injured his mother while the other injured 75-year-old Esperanza Herrera. The package that killed Mason detonated inside of his family’s home at 6:44 a.m.

“One of the residents went out front, and there was a package on the front doorstep,” Manley stated. “They brought that package inside the residence, and as they opened that package, both victims were in the kitchen, and the package exploded, causing the injuries that resulted in the young man’s death and the injuries to the adult female.”

Hours later, the second blast was reported at Herrera’s home after she found the package on her porch. When she picked up the package, it detonated. Police believe that the third bomb was not meant for Herrera but her neighbor, Erica Mason, who is not related to the Mason family but shares their last name and may have been targeted under the impression that she was related.

According to ABC News, the explosives “displayed a level of sophistication, indicating that the bomb-maker or bomb-makers were highly skilled.” The devices were designed to be detonated by motion like shaking or jostling, which is why they exploded when they were picked up. They also supposedly had some sort of safety switch, enabling the bomber to move the devices without blowing them up.

“There’s a certain level of skill and sophistication that whoever is doing this has, and... we are hoping to use the evidence we have to track them down based on what we are seeing on all three scenes that seem to be consistent,” Manley to KXAN news on Tuesday.

The police reported in an update to the media on Thursday that the bombs were made from a common materials readily available in most hardware stores, making the identification of suspect more difficult than if specialty materials had been used.

Though the Austin police agree that the bombings are related, they have yet to suggest a motive or a suspected perpetrator. They also have not said whether they think the victims were personally targeted. Manley did tell reporters that police are not ruling out the possibly “that hate crime is at the core of this.”

Police and local community leaders have stated the package bombs appear to have targeted members of prominent black families with close connections. The president of the local NAACP told NBC News that House and the Mason family knew each other and went to the same church.

Mason has been described as a talented musician who had been accepted into the University of Texas Butler School of Music. His grandmother LaVonne Mason is a co-founder of the Austin Area Urban League, a local civil rights organization.

House’s stepfather, Freddie Dixon, is close to Mason’s grandfather, Dr. Norman Mason, and was the longtime pastor at Wesley United Methodist Church, a predominantly black church in Austin that was founded by newly freed slaves in 1865.

“It’s not just coincidental. Somebody’s done their homework on both of us, and they knew what they were doing,” Dixon told the Washington Post. “My diagnosis: Number one, I think it’s a hate crime. Number two, somebody’s got some kind of vendetta here.”

The as yet unsolved bombings have placed the city’s residents on edge. Since Monday some 500 suspicious packages have been reported to the police throughout the city, though none of them have turned out to contain explosive devices.