This type of evidence is becoming increasingly important. Some CCTV cameras actually witness the crime itself - in those cases it is important to find out if the camera's time code is correct. Other merely show when the victim was last seen - in many cases a good guide to the time of the incident. Police make regular checks on CCTV cameras - and the evidence should be in the prosecution disclosures to the defence "if they are relevant". However, you will need to check all CCTV cameras for yourself - demand all those tapes or discs that the police hold , but also check if there are any other cameras around the scene. The police tend to use only those on their lists - the public ones. But there are private CCTV cameras around which might provide a different story to your advantage.
Tourist cameras, or other "private cameras" may well also provide information in certain circumstances. Remember that the time code on these cameras is normally set by the operator - perhaps not even on the day of the incident. This should be checked off against the real time to allow for any divergence. During the O.J. Simpson case in Los Angeles, the defence made great use of the cameras used by the TV units at the scene in order to determine when the police did certain things at the scene. The prosecution failed to interview any of the cameramen - all of whom would have set their camera "time of day" time codes by their watches before they set out from the office that day. It is common to find that no two professional cameras are set to the same "time of day" time code exactly.