Inside the 'fatal mistake' that led police to the Austin parcel bombing suspect

Inside the 'fatal mistake' that led police to the Austin parcel bombing suspect

Inside the 'fatal mistake' that led police to the Austin parcel bombing suspect

Updated 22 March 2018, 13:20 AEDT

Here is how authorities obtained the suspected parcel bomber's phone number, linked it to the bombing locations and zeroed in him after after 19 days, two dead victims and more than 1,000 calls of suspicious packages around the city.

One of the largest bombing investigations in the US since the Boston Marathon attacks in 2013 came to an intense close when authorities closed in on the suspected Austin parcel bomber.

The suspect, named as 23-year-old Mark Anthony Conditt, blew himself up as a SWAT team moved in after a 19-day bombing campaign that left two people dead and terrorised the Texan capital.

Police said a 25-minute video "confession" was uncovered on Conditt's phone.

"He does not at all mention anything about terrorism, nor does he mention anything about hate, but instead it is the outcry of a very challenged young man, talking about challenges in his personal life," Austin Police Chief Brian Manley said.

Here's how authorities zeroed in on their suspect.

Getting the mobile number

Tracking down Conditt started with police obtaining Conditt's mobile phone number.

This breakthrough came after he was linked through a licence plate number to a red truck spotted on surveillance video at a FedEx post office, where he is suspected to have dropped off a parcel bomb.

Conditt had been careful to avoid cameras before entering the post office this week disguised in a blond wig and gloves, said US House Homeland Security chairman Michael McCaul.

Mr McCaul said going into the store was Conditt's "fatal mistake".

He said once investigators linked Conditt to the license plate, it gave authorities a mobile number they could track.

Conditt sent at least two bomb parcels via post, one of which blew up on a conveyer belt in a sorting facility on Tuesday.

Number shower up at key bombing locations

McCaul said Conditt had turned off his phone for "quite some time" but that police pounced when he switched it back on.

"He turned it on, it pinged, and then the chase ensued," McCaul said.

Texas Governor Greg Abbott said police were able to closely monitor Conditt and his movements for about 24 hours before his death.

The Governor said the phone number was used to tie Conditt to bombing sites around Austin.

"The suspect's cellphone number showed up at each of the bombing sites as well as some key locations that helped them connect him to the crime," Mr Abbott said.

How did authorities track the number?

Once investigators had Conditt's phone number, they most likely contacted his carrier to track where the device's signal was connecting to towers.

But the authorities may have also tried to get an even more precise location by using "cell-site simulators" that act as fake towers.

These simulators, also known as "StingRays", broadcast radio signals stronger than legitimate mobile towers to force all phones within a targeted area to connect to them.

Some simulators can fit in the trunk of a police car that can cruise around a neighbourhood in an effort to find a certain phone.

But in the process they can also scoop up the locations of other phones, as well as personal data stored on them, said Stephanie Lacambra, a lawyer for the Electronic Frontier Foundation, a digital rights group.

Children at play sign and bomb-making materials

Authorities say they also tracked down Conditt through witness accounts and purchases made at hardware store Home Depot, where Mr McCaul said the suspect bought nails and other bomb-making materials.

Mr Abbott said Conditt's purchases at the store also included five "children at play" signs, one of which was used to rig a tripwire that was set off by two men Sunday in a southwest Austin neighbourhood. One of them was walking and the other was riding a bike.

William Grote told The Associated Press that his grandson was one of the victims and had nails embedded in his legs from Sunday's explosion.

On Wednesday, experts from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) discovered bomb parts similar to those used in the attacks at Conditt's home.

"I wouldn't call it a bomb-making factory, but there's definitely components consistent with what we've seen in all these other devices," Fred Milanowski, special agent in charge of the ATF's Houston field division, told reporters.

Investigators detained two of Conditt's roommates who lived at the home, the Austin Police Department said. One was questioned and released and the other was still being questioned. Police said their names would not be released because they were not under arrest.

Wires/ABC