Austin bombings: Texas police investigate 'connected' explosions after two injured in fourth blast within weeks

Two men have been injured in an explosion in Texas that police believe was linked to three other blasts this month.

Authorities said a tripwire may have been used to activate the device in the Austin suburb of Travis County, where families have been urged to stay indoors as investigators search for possible other bombs.

Two people were killed and two others wounded by three package bombs detonated elsewhere in the state capital in the past three weeks.

Austin Police Chief Brian Manley said officers were “working under the belief” that all four bombings were connected and have not ruled out a possible racist motive.

The latest blast, at 8.30pm local time on Sunday, took place in the south-west of the city, miles from the earlier three in eastern residential areas.

It is thought to have been caused by “a suspicious package that was left on the side of the road” and detonated by “someone either handling, kicking or coming into contact with a tripwire”, Mr Manley said.

Both wounded men were riding or pushing bikes when the blast went off, he added. They were taken to hospital with injuries that are not thought to be life-threatening.

The three earlier explosions were all caused by package bombs left overnight on the doorsteps of victims’ homes.

The first killed 39-year-old Anthony Stephan House at his north-east Austin home on 2 March. Two more bombs exploded further south in the city on 12 March, killing 17-year-old Draylen Mason, wounding his mother and injuring a 75-year-old woman.

Mr Manley has suggested the bombs could have been hate crimes, since all the victims were black or Hispanic. But he said investigators were not ruling out any possible motive.

"We're working on belief that they are connected," he added.

In a hastily organised early-morning press conference close to the site of the fourth blast, the police chief warned residents within half a mile of the latest explosion to remain in their homes until 10am.

“We’re asking the residents to stay inside so that we can do our best to ensure that there are no other devices,” he added.

“It is very possible that this device was a device that was activated by someone either handling, kicking or coming into contact with a tripwire that activated the device.

“We now need the community to have an extra level of vigilance and pay attention to any suspicious device, whether it be a package, a bag, a backpack – anything that looks out of place – and do not approach it.”

He said “projectiles” of some kind appeared to have been packed into the bomb to injure victims.

No one has been arrested in connection with any of the blasts, which are also being investigated by FBI agents and the US Bureau of Alcohol, Tobacco, Firearms and Explosives.

Authorities have offered a reward of $115,000 (£82,000) for information that leads the arrest of the culprit.

Earlier on Sunday, police said whoever was behind for the bombs may be trying to send a message. Mr Manley urged the bomber to contact authorities to explain any motive.

"We are not going to understand that until the suspect or suspects reach out to us to talk to us about what that message was," he said.

Mr Manley last week urged residents receiving unexpected packages to call authorities without touching or opening them. Police subsequently responded to at least 735 calls about suspicious packages but did not find anything dangerous.

A city centre gig by hip-hop band The Roots, scheduled as part of the South By Southwest music festival, was cancelled on Saturday night after a bomb threat. Authorities later arrested a 26-year-old man but said the incident did not appear to be related to any previous explosions.