(CNN) Ten Philadelphia police recruits resigned last week after their plot to cheat on an exam was revealed by another recruit, the police department said in a statement.

One of the recruits obtained answers to a department test and then distributed them to nine other members of the same platoon, police said.

Another recruit, who witnessed the cheating, reported the plot to higher-ups, who launched an internal investigation, according to the department.

Philadelphia police Capt. Sekou Kinebrew told CNN affiliate KYW that the exam on motor vehicle code would have been open-book.

All 10 recruits resigned near the investigation's end, before any of them took the exam, police said. If they hadn't resigned, the police department said, the recruits would have been rejected from the force.

Read More