"The American dream was my conception of happiness, and from reading the Bible, I was showed that those things wouldn't make me happy,'' Rooney, 24, said in an interview with The Denver Post.
"My life had no true love, no true joy and no true peace.''
Raised near Boston, Rooney was a 22-year-old environmental-science major at Humboldt State University in northern California when he joined the group in October 1996.
Back then, Rooney was an avid skier and snowboarder. An average student, his social life centered on parties and dating. He aspired to be a well-paid professional.
He was like a lot of college kids, Rooney said.
But Rooney's path veered dramatically when he met a member of The Brethren on campus and within several days abandoned everything he had known - including his family - to join the cult-like group.
Rooney said he and other members lead simple lives modeled on Jesus and the early disciples. They have forsaken their jobs, families, educations and worldly possessions to travel the country in small subgroups witnessing the Gospel.
Group members reject modern medicine, camp in the forest and eat discarded grocery-store produce, a practice that has earned them the nickname "The Garbage Eaters.''
The men ride homemade mountain bikes and wear unkempt beards and tunics. They earn the little money they need by repairing bicycles.
The group's appeal is its offer of a newfound relationship with God, the polite and soft-spoken Rooney said.
"Christ said to seek first God and his righteousness. If I spend my days thinking about God and living a righteous life, being pleasing to him, then he's got everything worked out,'' Rooney said, while tugging thoughtfully on his sparse beard.
Parents had him arrested
"The benefits of living day to day are that I don't have to worry about tomorrow.''
With a quiet laugh, Rooney admitted his life is unusual. And in recent weeks, it has taken another bizarre turn.
His estranged parents, Mickey and Dorothy Rooney, had their son arrested in Fort Collins after he arrived in the northern Colorado city on a recruiting mission with four other members of The Brethren.
The Rooneys, desperate to regain their son from the group, invoked an outstanding arrest warrant for larceny issued in their hometown of Wilmington, Mass., authorities have said.
Arrested on Aug. 10, Rooney is being held at the Larimer County Detention Center in lieu of $5,000 bail. He is awaiting extradition to Massachusetts to face a charge that he stole more than $250 from his father, an allegation Patrick firmly denies.
The Rooneys' cross-country search for their son was detailed on a segment of "PrimeTime Live,'' which aired last spring and was rebroadcast last week. The couple have declined to talk to reporters since Patrick's arrest.
The Rooneys have twice spoken to their son at the Fort Collins jail. But Patrick rejected his parents after his mother mentioned that she would keep following her son as long as he continues his unquestioning devotion to The Brethren, he said.
Echoing other group members interviewed, Rooney said he won't communicate with his family unless they accept his religious beliefs and his lifestyle.
But the lifestyle Rooney called "honest and pure'' is viewed by parents as precarious and potentially unhealthy.
Deserted parents and cult experts across the country have said members are controlled by their church elder, an ex-Marine named Jim Roberts who formed his group in 1971.
Roberts travels the country like his followers, estimated to number 100. Parents who track the group said Roberts recently has been in California and Ohio and now is thought to be in New York.
While he does not coerce money or belongings from recruits, Roberts maintains control over his flock by teaching that their true family members are not blood relatives but other disciples of God, the group's watchers said.
"The Roberts group is a cult, and they're a cult because they immediately destroy relationships to keep those kids in there. It's the glue that holds the cult together,'' said Larry Wilcox of Bozeman, Mont., who has been searching for his son, Bart, for more than seven years.
Indeed, Rooney said he has replaced his family with the Roberts group.
But contrary to parents and cult experts, Rooney insisted he made the choice of his own free will.
"I wasn't influenced at all,'' he said.
"I want to give my whole life to God. I don't want to keep anything back.''
However, parents and experts who follow the group said they are convinced that Rooney and others would change their minds if they fully understood the group's psychological dynamics.
" "My life was empty and now I'm full' is pure cult indoctrination. They could have found meaning without Jim Roberts and his twisted Scriptures,'' Wilcox said.
Countered Rooney: "I want to be happy, and I've been happy ever since I did this.''