One of the Baltimore police officers who arrested Freddie Gray wants the police department and prosecutor to produce a knife that was the reason for the arrest, saying it was an illegal weapon.

The city's top prosecutor, Marilyn Mosby, said Friday in charging the officer and five others that the knife was legal under Maryland law. She said that meant the officers had arrested Gray illegally.

The motion was filed Monday by attorneys for Officer Edward Nero in Baltimore District Court.

Nero is charged with second-degree assault, misconduct in office and false imprisonment.

He argues in his motion that the knife found in Gray's pocket — described in charging documents as "a spring assisted, one hand operated knife" — is illegal under stricter rules in Baltimore.