I agree with you. This has been a problem within the law enforcement community itself for some time. Not only with unmarked vehicles but with police officers in plain clothes. There has been some pretty serious mistakes made due officers shooting officers, one about 25 years ago resulted in a municipal bankruptcy which got the attention of State, Department of Laws nationwide concerning safety agency mutual aid agreements. More pertinent remedial law enforcement alternatives need to be considered and developed by managers then initiated, other than just eliminating these useful law enforcement tools. 

In this case, if the allegations prove to be correct, the employee needs not only to be discharged of employment but possibly indicted with a criminal mischief charge.