CNN reports that investigators believe a bomb at a FedEx just outside of San Antonio may be linked to four explosions in Austin this month. At the incident on Tuesday morning, one FedEx employee was injured at the ground sorting facility. According to the company, it was a “single package” explosion.

The four explosions that have happened in Austin this month have killed two and injured four more since March 2.

Although investigators are looking into whether this latest explosion is connected to the Austin explosions, this is the first one to use the method of mailing a package.

In the first three explosions in Austin, there were packages left in front yards and porches that were not sent via any mail service. The fourth blast was tripped by a tripwire and injured two men, according to police.

The Congressional Black Caucus is calling for elected officials to classify the explosions as terrorist attacks and determine if they may have been racially motivated.

More than 350 federal agents are assigned to the case, as well as 100 state officers and agents.

Evidence from the first four blasts in Austin is being investigated in Quantico at the FBI headquarters. Agents are looking for similarities, and believe at this point they were all created by the same individual or group.

The first three explosions were aimed at members of minorities, so they could be hate crimes. However, a motive has still not been determined. Two white males were injured in the fourth explosion via a package on the roadside, making police believe that it was not directed at a specific person or group.

The use of the tripwire in the fourth blast in Austin tells police the suspect or suspects may be more sophisticated and capable of building complex bombs, says law enforcement.

*Photo credit Eric Gay/AP