Questions have been raised about Ahmad Khan Rahami's trips to Afghanistan and Pakistan
The father of the New York-New Jersey bomb suspect has said he had "no idea" of what he had been planning.
"I'm not sure what's going on exactly. It's very hard right now to talk," Mohammad Rahami told NBC News.
His son, Ahmad Khan Rahami, has been charged with five counts of attempted murder.
The charges, which also include weapons offences, stem from a gun battle with police in which the 28-year-old naturalised US citizen from Afghanistan was taken into custody.
The FBI said Rahami was wanted in connection with a pipe bomb blast in New Jersey on Saturday morning and the detonation of a pressure-cooker bomb in Manhattan that evening that injured 29 people.
A second unexploded device was found close to the scene of the New York blast. Prosecutors say they are still considering charges over the bombings.
Surveillance video from the night apparently shows the suspect dragging a bag, moments before an explosion in Manhattan's Chelsea district.
After being captured on Monday, Rahami was pictured on a stretcher being taken into an ambulance, with a bloodied bandage on his right arm and moving his head from side to side with his eyes open.
Since being detained, Rahami, who was not on US anti-terrorism databases, has undergone surgery for a gunshot wound to the leg.
The suspect, who is being held on $5.2m bail, was sleeping in the doorway of a bar when the owner reported him to police.
It has been reported that Rahami travelled to Afghanistan and Pakistan multiple times in recent years, with police considering whether he had been radicalised overseas.
Citing unnamed law enforcement sources, CNN said the trips included a year-long stay in Pakistan ending in March 2014.
CNN also reported that Rahami's wife left the US days before the explosions took place.
According to the New York Times, no evidence has yet been found that Rahami had military training overseas.
The paper said FBI agents were trying to find out whether his actions had been informed by Islamic State or another such organisation.
US security sources said Rahami had secondary screening after returning from overseas and passed every time.
Republican presidential candidate Donald Trump said the authorities should "use whatever lawful methods are available" to get information from him.