Four bombs have now gone off in Austin, Tx, over the last 17 days. The most recent was last night, a bomb triggered by a tripwire that left two men injured.

According to the FBI, this “changes things,” representing a significant step up in the sophistication of the device compared to the earlier bombs which left two African-American men dead and a hispanic woman critically injured. All four devices share similarities which suggest they are the work of the same bomb maker.

The first three bombs were all left at residences, disguised as delivered packages. All detonated as the victims were opening or handling them. The fourth bomb was left on a roadside in a different area of the city.

Because the first two victims were black, a 39-year-old construction worker and a 17-year-old high school student, both related to prominent members of Austin’s African-American community, the attacks have raised suspicion that they are racially motivated. The area where the first three bombs went off were neighborhoods east of I-35, the six-lane highway which divides the affluent and predominantly white west side of the city from where black and hispanic residents have historically lived on the east side.

The fourth bomb, however, breaks from that pattern. It was planted in the city’s southwest. The two men injured in the blast are both white.

So where does that leave us? Can we describe these as acts of terrorism?

Four bombs have now gone off, all apparently the work of the same individual or group of individuals. The attacks have left the city on edge, with police urging the public to be alert for suspicious packages. The neighborhood where the fourth bomb went off was placed on lockdown until this afternoon, with residents kept in their homes and school buses ordered to stay away. The identities of the first three victims suggest a possible motivation.

That last is the key to understanding whether or not what is happening in Austin constitutes terrorism or something else. Definitions of terrorism typically focus on several key elements: threat or use of violence; intention to create fear in an audience beyond the immediate victims of an attack; all in the service or pursuit of some political/social/religious motivation or objective.

So that’s what we still need to know about the Austin attacks. Until we find some further evidence of common ideological motivation connecting the bombings, we will have to reserve judgment.