earlier today that he has no regrets in voicing his disapproval over the handling of Bradley Manning, the man accused of leaking secret cables to WikiLeaks.
Mr Crowley told the HARDtalk programme that the treatment of Bradley Manning was undermining "a very legitimate" effort to prosecute him.
Pte Manning has been held in shackles in solitary confinement.
Mr Crowley left the department after calling his treatment "stupid".
"I thought the treatment of Bradley Manning was undermining what I considered to be a very legitimate prosecution of an individual who has profoundly affected US national security," Mr Crowley said in his first public remarks since stepping down on 13 March.
He said he had not anticipated his criticism of another arm of the US government - the military - would spark such a controversy, and said it was appropriate for him to step down because his remarks had put President Barack Obama in a "difficult position".
"Quite honestly I didn't necessarily think the controversy would go as far as it did but I don't regret saying what I said," Mr Crowley said.