As was stated, if the police have lawfully obtained the video they can use the data for whatever lawful and appropriate purpose they see fit. if they observe evidence of an unrelated crime, they can use that as well. They can run the license plates of vehicle observed in the video provided the information is for a law enforcement purpose and not simply because the reviewing technician though the driver was hot and wanted to know how to find her.
The data extracted from evidence can be used by the police for whatever lawful purpose might be necessary ... subject to laws or policies that might restrict redistribution of the data within.the

