The father of the man charged with setting off bombs in New York and New Jersey informed the FBI in 2014 about his son's apparent radicalisation, he said.
Mohammad Rahami, father of alleged bomber Ahmad Khan Rahami, said his son underwent a personality shift after visiting Afghanistan and Pakistan in 2013.
Her said his son was not the same after that trip.
"I found a change in his personality. His mind was not the same. He had become bad and I don't know what caused it but I informed the FBI about it," he said.
Mr Rahami Snr said he was not sure if the FBI took any action against his son at the time and said he and his family were in a state of shock following last weekend's blasts, which injured 31 people.
"I condemn the act of my son and I am sad over injuries caused to people," he said, adding that he was cooperating fully with investigators.
Rahami, an Afghan-born US citizen was shot and severely injured during his arrest on Monday. He has been unconscious for much of the time since undergoing surgery, said Robert Reilly, a spokesman for the FBI's Newark office.
Prosecutors say Rahami, 28, planned the explosions for months as he bought components for his bombs online and set off a backyard blast. They say he wrote a journal that praised Osama bin Laden and other Muslim extremists, fumed about what he saw as the US government's killing of Muslim holy warriors and declared "death to your oppression".