Authorities in Texas are investigating a suspicious package at a FedEx facility near the global airport in Austin. It was a powerful device, essentially a pipe bomb, in a normal-size delivery box, which would be a theme for the first three bombings.
The explosion Tuesday night unfolded on Brodie Lane in southwestern Austin.
"If this bomber is being motivated, in part, by the sense of power and control that he has holding the city of Austin in a state of fear, and depending how addictive that feeling is", she said, "that can be a strong contributor to his doing it again and not waiting a long period of time".
The latest Austin blast occurred Sunday evening when two men received non-life-threatening injuries after apparently setting off a tripwire in the southwest of the city.
One worker was injured after the package - which was destined for Austin - exploded at the facility near San Antonio, on 9935 Doerr Lane, in Schertz, TX, after midnight, police said.
The FBI, state, and local authorities are investigating both incidents. Authorities would not confirm media reports that the package contained metal shrapnel and nails.
If the FedEx incident is confirmed to be linked to the Austin blasts, it would represent a new method for the bomber or bombers.
More than 1,200 Austin residents have contacted police since the morning of 12 March to report suspicious packages, police said. They suffered what police said were significant injuries and remained hospitalized in stable condition. He said that federal law enforcement was already working with local officials to identify the source of the attacks.
The FBI says it's "more than possible" the blast is linked to the recent ones in Austin. Police said they are investigating whether the bombings were hate crimes.
ATF and Federal Bureau of Investigation agents were on the scene, along with SWAT and bomb squads and the Schertz Police Department.
Police and federal agents had said that the blast triggered along a street by a almost invisible tripwire suggested a "higher level of sophistication" than they had seen in the three earlier package bombs left on doorsteps, and meant the carnage was now random, rather than targeted at someone in particular.
One person was lightly injured but did not require treatment, police said.
A fifth explosion happened in the early hours this morning, but the distance and nature of the blast differ from the earlier instances.
Austin police have offered a $100,000 (£71,340) reward for information, and Texas Governor Greg Abbott has offered an additional $15,000.
Two people have died and four others have been injured in package bomb explosions in Austin this month.
A fourth package bomb explosion on Sunday night in Texas left two more people injured.
A Sunset Valley Police officer at the scene told KXAN's Alyssa Goard said the package that exploded at the Schertz facility was shipped from the Brodie location.