Newly unsealed federal documents reveal the suspected Austin bomber used a PVC tube with a metal pipe inside surrounded with shrapnel in his attacks that killed two people and seriously injured four others.

Investigators identified Mark Conditt as the suspect by pairing identical components found in the six bombs with surveillance footage of him buying this material, according to an affidavit used to support his arrest warrant.

Officials also said on Monday they do not believe the victims of the bombings were linked and are yet to say whether they have established any motive for Conditt's terror spree.

Investigators identified Mark Conditt (left in an undated photo) by matching the components in his bombs, it was announced at a news conference on Monday, where U.S. Attorney John Bash (right) also said his victims were not linked

FBI agents and alcohol, tobacco, firearms and explosives police at the scene of an explosion on March 12, which injured one person

Over three weeks, starting on March 2, six package bombs were left at people's doorsteps in Austin, concealed along a walking path, or sent via FedEx, in seemingly random attacks.

Two African-American males, including a 17-year-old boy, were killed, and a Hispanic woman and two white men were injured when they picked up or opened the packages, or stumbled over a tripwire.

On February 27, four days before the first bombing, 23-year-old Conditt used his credit card to buy five battery holders with snap connectors from a Fry's Electronics store in the Texas state capital.

All the bombs used the same battery holders that Conditt purchased, according to the affidavit. He also bought nails for shrapnel at the Home Depot but purchased the batteries online.

Fred Milanowski released the now-defunct affidavit for Conditt's arrest at the conference on Monday which revealed all of his bombs consisted of a PVC tube with a metal pipe inside surrounded by shrapnel

Surveillance footage was also located showing a man who looked like Conditt visiting a Home Depot to buy a 'Drive Like Your Kids Live Here' sign.

Investigators believe a similar sign was used in fourth explosion on March 18, which injured two people using a tripwire. A witness told officers they left their house and returned to see the sign, which they had not noticed before.

On March 18, the suspect also bought a six-pack of work gloves matching the ones seen in a video taken from a Sunset Valley FedEx Office store showing him sending two of the package bombs while wearing a wig and a hat.

A store worker who was later interviewed by federal investigators said he saw Conditt drive off in a red truck, which was similar to the Ford Ranger which he was known to use.

One of the packages exploded at a FedEx facility in Schertz on March 20. The other was found at a FexEx site in Brodie Lane, where an x-ray revealed the same battery holders Conditt bought on February 27.

The bomb itself was shown to consist of a PVC tube with a metal pipe inside surrounded by shrapnel, in common with the other devices.

The document still redacts details about some of the witnesses who were interviewed and the exact trigger Conditt used, which was designed to go off when the flap of the package was opened.

The suspect also bought a six-pack of work gloves matching the ones seen in a video taken from a Sunset Valley FedEx Office store showing him sending two of the package bombs while wearing a wig and a hat (pictured on March 18)

Conditt, an unemployed man from the Austin suburb of Pflugerville, died on March 21 after blowing himself up as police ran towards his vehicle, which is pictured being towed away from the scene a day later

Conditt, an unemployed man from the Austin suburb of Pflugerville, died on March 21 after blowing himself up as police ran towards his vehicle.

In a video confession found on his cellphone, Conditt detailed how he made seven bombs. Five exploded, one was recovered before it went off and a seventh he detonated that killed him.

John Bash, U.S. attorney for the Western District of Texas, announced on Monday that although investigators were still ongoing he did not believe the victims were linked.

'The investigation into motive and intent is ongoing. I have not seen information so far to believe that there is a common link between the victims,' he told a news conference.

At this point, authorities do not intend to release the confession, voicing worry it could inspire others.

Investigators work by the side of a road in Travers County, Texas, on March 19 where a day earlier a bomb went off injuring two people

FBI agents collect evidence at a FedEx Office facility following an explosion at a nearby sorting center in Sunset Valley on March 20

Law enforcement officials search for evidence at the location where Conditt blew himself up on March 21

'The subject in the audio confessions says a number of statements that concern us. We just don´t want that to live forever on the internet,' said Fred Milanowski, special agent in charge of Houston Field Division for the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF).

'From the review of past criminals, we are very concerned, and the last thing we want is this to inspire somebody else,' said FBI special agent Christopher Combs, who has been in charge of the federal agency's response.

Authorities on Monday also dropped a federal charge against the deceased bomber, involving receiving, possessing and transferring a destructive device, according to a criminal complaint.

Conditt pictured in a 2010 student ID photo released by Austin Community College

'Multiple other individuals were investigated for potential links to these destructive devices.

'None of those persons were deemed likely to be involved,' a redacted arrest affidavit released on Monday said.

Two roommates of Conditt were questioned and released from custody.

US Attorney John Bash said investigators were looking through Conditt's 'voluminous computer records' for additional clues.

'The investigation continues. We're looking at his intent, his motivations,' Bash told the news conference.

The Austin American-Statesman reported in March that Conditt described himself on the confession recording as a 'psychopath' who had been disturbed since childhood.

'I wish I were sorry but I am not,' Conditt said, according to the newspaper.

The college dropout was also part of a Christian survivalist group called Righteous Invasion of Truth RIOT) that would discuss weapons and dangerous chemicals.