Robert Crawley, 14, was being quizzed by police after he was arrested during a massive manhunt. He was detained without incident, along with another boy aged 16, at a house in High Wycombe, Buckinghamshire, shortly after 10am.
The four weapons, two .22 calibre rifles and two .22 calibre handguns, were stolen from Peter Preston, 67, on Friday, after the boy's disappearance. They were kept in a secure box at Mr Preston's sheltered house close to the boy's home at Chalfont St Peter.
Mr Preston, a member of Wendover Shooting Club, admitted he would probably not be allowed to keep the weapons, which were the subject of much interest to local youngsters.
Armed police had spent the weekend hunting for the boy who has learning difficulties.
Tracker dogs and a helicopter were used after a report that a motorist was shot at. He was badly shaken but unhurt.
The incident, less than a week after the massacre at Dunblane, sparked fears of a copycat attack. Plain clothes officers were deployed at three local schools.The two boys were arrested as they left a house unaware they were being watched by police, acting on a tip-off.Reuse content