Investigators say they have discovered a 25-minute recording left behind by alleged Texas bomber in which he confesses to the crimes.

The discovery came just hours after 23-year-old Mark Conditt, accused of a three-week bombing campaign in Texas that killed two people and injured five others, blew himself up after a standoff with police.

Austin police chief Brian Manley told a media conference on Thursday that Conditt’s recording, made on a mobile phone, described the devices he used during the bombings.

“I would classify this as a confession,” Mr Manley said.

The phone was found in Conditt’s possession after his death.

Mr Manley said the motive for the bombings and why specific people were targeted may never be known.

“We’re never going to be able to put a [reason] behind these acts,” he said.

“But what I can tell you, having listened to that recording, he does not mention anything about terrorism, nor does he mention anything about hate.

Instead, it’s the outcry of a very challenged young man talking about challenges in his life that led him to this point.”

“The deaths that occurred here were random and meaningless and something that we can’t ever get our heads around,” Ms Moore said.

Mr Manley earlier said police tracked Conditt to a hotel about 32 kilometres north of Austin and followed him when he pulled to the side of the road and detonated a device, killing himself.

He said Conditt set off a bomb as two Austin police officers approached the vehicle.

Mr Manley said the recording was the outcry of a ‘challenged’ young man. Photo: AP

Conditt’s family released a statement expressing shock and grief, as well as offering “prayers for those families who have lost loved ones … and for the soul of our Mark”.

Conditt attended Austin Community College (ACC) before dropping out before graduation in 2012.

According to a Facebook post by Conditt’s mother, reviewed by TIME magazine before it was deleted, he was homeschooled until 2013 and was planning a possible religious missionary trip.

Conditt also created a blog about his political views as a requirement for a political-science class he took at ACC, detailing views against gay marriage, on “free abortion” and sex offender registration stances, as well as an argument for the death penalty.

“Homosexuality is not natural. Just look at the male and female bodies. They are obviously designed to couple,” he wrote in one of the posts.

In the blog’s biography, he described himself as a conservative who enjoyed cycling, parkour, tennis, reading and listening to music.

Conditt was the oldest of four children and reportedly worked at a manufacturing company, but was dismissed last August because he wasn’t meeting expectations.

As authorities continue to search for more possible explosive devices, police recovered homemade bombs from inside the home that Conditt shared with two other men.

The Austin Police Department and federal authorities said in a statement that they were “working to safely remove and dispose of” the explosives at the home.

Authorities evacuated four blocks around the building “in an abundance of caution”.

Conditt blew himself up inside his vehicle as police approached his vehicle. Photo: AP

Police earlier detained the two people who lived with Conditt.

Austin police said Wednesday that one roommate was questioned and later released, while the second was still being held for questioning.

Authorities did not release the names of the roommates, explaining that they had not been placed under arrest.

Four bombs exploded in Austin since March 2, killing two men and injuring four people.

A fifth bomb exploded early Tuesday at a FedEx sorting facility in Schertz, about 100 kilometres southwest of Austin.

A package containing what was believed to be an unexploded bomb was found Tuesday at a FedEx distribution centre in Austin.

-with agencies