Universal Pictures has purchased screen rights to "Public Enemies," the bestselling book by "Barbarians at the Gate" author Bryan Burrough.
The pic will tell the story of how the government's attempt to stop Depression-era criminal legends John Dillinger, Baby Face Nelson and Pretty Boy Floyd transformed J. Edgar Hoover's FBI from a powerless agency into the country's first federal police force.
It is unclear yet which role DiCaprio will take, or even which side of the law his character will be on.
Mann is expected to direct another film while the crime saga is being scripted. DiCaprio is starring in the De Niro-directed The Good Shepherd and will follow by starring with Matt Damon in Martin Scorsese's The Departed.