If Config.UseFingerprintSystem is enabled, police officers must first collect the person's fingerprints using the fingerprint scanner before the DNA shows the character's name.
If you do not want this behavior, you can disable it by setting:
Config.UseFingerprintSystem = false
in the config file.
UV light not working
The UV light is only meant to be used inside vehicles. Normal evidence can be seen with the regular flashlight (WEAPON_FLASHLIGHT)
Fingerprints inside a vehicle will only appear if:
Another player (who is not police) has been inside the vehicle
The player was not wearing gloves
If those conditions are not met, no fingerprints will be found.