Manchester suicide bomber Salman Abedi was known to police in his teenage years for theft, receiving stolen goods and assault but not for holding extremist views, according to Greater Manchester Police.
GMP chief constable Ian Hopkins said Abedi appeared on police logs in 2012, when "he would have been 16 or 17", for what he described as a "relatively minor" criminal record.
But he said the 22-year-old attacker was "not known" to the government's Prevent counter-terrorism strategy and "was not on any sort of Prevent agenda".
MI5 is understood to have launched two urgent inquiries into whether it missed the danger posed by Abedi amid claims it was warned he was planning a terror attack.
A senior Whitehall source previously said Abedi was a "former subject of interest" to the security services whose risk "remained subject to review".
Mr Hopkins mentioned Abedi's criminal record in reply to a question during a phone-in with BBC Radio Manchester, which saw him asked: "How can somebody slip through the net that's already on the radar to commit such an offence?"
Mr Hopkins replied: "Obviously there has been a lot said in the media and what I would just say to people is just be careful of some of the reporting that is going on because obviously we don't know everything at this stage.
"So what I do know about Abedi, the terrorist, is that he was known to the police for some relatively minor matters, theft, receiving stolen goods, minor assault. Those were in 2012."
He added: "Now of course we continue to check records going back and the Home Secretary announced (on Monday) that the security service are going to review what they knew as well.
"Obviously I am not privy to what the security service did or didn't know about that individual at this time. But from a police perspective that's what I knew."