Texas - A package exploded early Tuesday at a FedEx distribution facility in Texas, authorities said, following a series of other blasts in Austin in recent weeks that police had attributed to a serial bomber.The parcel exploded at a facility in the town of Schertz, in the San Antonio area.In a statement on social media, the Schertz Police Department said one person received medical attention at the scene."We can confirm that a single package exploded while in a FedEx Ground sortation facility early this morning," the shipping company said."One team member is being treated for minor injuries. We are working closely with law enforcement in their investigation."The Washington Post, quoting the FBI, reported that the package had been bound for Austin, the state capital - scene of previous deadly blasts.The explosion came as hundreds of police officers and FBI agents searched for the perpetrator of Sunday's blast in Austin - the fourth this month - left two young men seriously injured and the city on edge.Police said that blast was connected to three previous bombings in Austin. They said the bomber used a tripwire in Sunday's attack."We're clearly dealing with what we expect to be a serial bomber at this point," Austin police chief Brian Manley told reporters.But Manley said police have been unable to determine a motive for the bombings.The four blasts in Austin killed two people in the city of nearly one million people and injured another four."Is this terrorism? Is it hate-related?" Manley asked. "As we said from the very beginning, we were not willing to classify this as terrorism, as hate, because we just don't know enough."In the earlier bombings, two African American men were killed by packages left on their doorsteps, raising speculation of a racially motivated crime. A 75-year-old Hispanic woman was also injured in a blast.But Manley said Sunday's bombing also seriously wounded two white men aged 22 and 23 as they walked in a quiet residential neighbourhood.He said it appeared random and was triggered by a tripwire.Manley said the use of a tripwire also means police are dealing with someone who "shows a higher level of sophistication, a higher level of skill" than initially believed.Manley appealed to the bomber to contact the authorities and to the public to report anything suspicious."I will reach out to the suspect or suspects and ask that you contact us, ask that you reach out to us, communicate with us so that we can put this to an end," Manley said."There are innocent people getting hurt in this community and it needs to come to a stop."The authorities said they were increasing the reward offered for information leading to an arrest, bringing the total city and state bounty money to $115 000.An exploding package killed 39-year-old Anthony House on March 2. A 17-year-old African American, Draylen Mason, was killed on March 12 and the Hispanic woman was critically injured the same day.All of the cardboard packages were hand-delivered and the bombs were built with household items available at hardware stores.A task force of hundreds of law enforcement personnel is working the case, including criminal profilers and experts from the Federal Bureau of Investigation and the Bureau of Alcohol, Tobacco and Firearms (ATF).