A 16-year-old boy is being questioned by police after being arrested on suspicion of taking part in a robbery at a bank.
A branch of Lloyds in London Road, Headington, Oxford, was raided at 10.30am on January 23, Thames Valley Police said.
The teenager, from Oxford, is in custody after being arrested on Friday.
Reports at the time said two men with their faces covered and dressed in blue boiler suits stole cash from the branch, with one believed to have a firearm.
No one was injured.
Thames Valley Police are appealing for witnesses and information.
A police spokesman said: "I would ask anyone who may not have contacted police already, but has any information about this robbery, to get in touch.
"Call 101 with information no matter how minor the detail may appear."
Anyone with information can also call Crimestoppers anonymously on 0800 555 111.