Austin serial bomber kills himself with explosive device: police

A 24-year-old suspected "serial bomber" who terrorised the US state of Texas, especially its capital Austin, for nearly three weeks with parcel bombs is dead after he blew himself up in his car as authorities closed in, police said today.

Austin has been on edge amid the attacks, which have led to the deployment of hundreds of police officers to the city.

Since the bombings started on March 2, investigators frantically searched for clues, calling the attacks the work of a "serial bomber" who increasingly changed tactics.

Two people were killed and six others injured in five bombings, terrorising the Texan capital with fear for 19 days.

The suspect, identified only as a 24-year-old white man, was killed after detonating a device when officers approached his car off a highway in the city of Round Rock, north of the state capital.

The incident follows four bomb attacks in Austin, the state capital, and one in Schertz, 104km south.

After using the Google search engine to gather information on the suspect's online browsing history, which showed searches on facilities which were used to ship packages, authorities later managed to locate his vehicle.

As authorities waited for tactical vehicles to arrive, the suspected bomber drove away and stopped in a ditch, Austin Police Chief Brian Manley said in an early morning press conference.

When members of the SWAT team approached, the suspected bomber detonated an explosive device inside his car, Manley said. One officer was knocked back and injured, and a second officer fired his gun, he said.

The suspect, who sustained extensive injuries from the explosion, died, Manley said.

In the most recent explosion before the suspect's death, a package exploded at a FedEx sorting center near San Antonio yesterday, and a second unexploded bomb was discovered on the same day at another FedEx facility near Austin.

Of the four previous explosions in Austin, the first three involved cardboard packages left in front yards or on porches. They weren't delivered by the US Postal Service or services such as UPS or FedEx, police say.

Those three explosions -- one on March 2 and two more on March 12 -- killed or wounded three African-Americans and one Hispanic person.

The explosions happened in east Austin areas with predominantly minority residents. Some residents expressed concern the attacks might have been racially-motivated, CNN reported.

Police have not ruled out the possibility that those bombings could be hate crimes. They urged residents to pay attention to their surroundings, and not approach or touch anything that looks suspicious.

"We don't know where the suspect has been over this past 24 hours," Austin police chief Manley said, adding that it was possible that additional devices may have been distributed.