Police believe Mark Anthony Conditt was behind six recent blasts that have killed two people and seriously injured four others.
Authorities finally found him on Wednesday, but he blew himself up in his car as officers closed in on him. Conduitt's motive remains a mystery.
A friend of the 23-year-old, who said he was close to him in 2012 and 2013, told the Austin American-Statesman newspaper that the suspected bomber attend Bible studies and church on Sundays.
Jeremiah Jensen said: "I know faith was a serious thing for him.
"I don't know if he held onto his faith or not. The kind of anger that he expressed and the kind of hate that he succumbed to — that's not what he believed in in high school. I don't know what happened along the way. This wasn't him."
His friend also described Conduitt as an assertive person who was "rough around the edges".
"He loved to think and argue and turn things over and figure out what was really going on," Jensen said.
Conditt's family released a statement saying they had "no idea of the darkness that Mark must have been in".
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