CHICAGO (CBS) — Federal prosecutors have dropped an escape charge against a convicted bank robber who broke out of the Metropolitan Correctional Center last month.

The U.S. Attorney’s office indicated it would be a waste of manpower to prosecute Joseph “Jose” Banks on the escape charge, since he’s already facing 80 years in prison for his bank robbery convictions.

However, criminal defense specialist Michael Ettinger said he thinks there might be more than that behind dropping of the escape charge.

“Probably because of the facts that would come out on how this occurred, that they don’t want the other inmates to know,” Ettinger said.

On Dec. 18, Banks and his cellmate, Kenneth Conley, escaped from the MCC – a high-rise federal jail in downtown Chicago – by breaking open the window of their cell and climbing down 15 stories on a makeshift rope of bedsheets.

Banks was captured three days later on the North Side. Conley remains at large, and the FBI has offered a $50,000 reward for information leading to his capture.

U.S. Attorney’s office spokesman Randall Samborn noted that the escape charge against Banks can be reinstated after he’s been sentenced on the bank robbery charges, if prosecutors believe that sentence is insufficient.