Anthony Rackley, 62, escaped from a Maryland prison in 1980 after being convicted of robbery. He later took on an alias and earned a living raising funds for the Lions Club community service organization.
"He called initially to report an extortion," Master Sargent Gary Knight of the Oklahoma City Police Department told Reuters on Friday.
"He called back and said he needed to talk to us about a situation. He said 'I'm a prison escapee from Maryland.' He was very forthright and forthcoming."
Going by the assumed name Jack Watson, Rackley told police his fundraising partner knew he was a fugitive and was demanding a large chunk of the money they raised for the charity to keep quiet.
When the man asked for additional money earlier this week, Rackley said he had had enough.
"He was willing to go back to jail to stop it," Knight said.
Authorities in Maryland are seeking Rackley's extradition, Oklahoma City police said. Oklahoma City police were investigating the business partner