Witnessing is an Enforcer only action. While in the Action Districts criminals all over are committing crimes. What kind of a cop would you be if you could not witness the crime and engage pursuit of the criminals?
To witness a crime: firstly you must be an enforcer, and second you must find a criminal that has committed a crime. A pair of handcuffs will appear next to the right of their name if they have broken the law. Ram-raiding, mugging civilians, and stealing vehicles are currently the crimes that can be "witnessed."
Once you see a criminal commit a crime you must point yourself at him and press Alt (Or whichever keybind you set "Witness" too) when the orange circle appears in your reticle. (Note: You need to be outside of your vehicle to witness a crime.)
This will generate a bounty mission for the enforcer faction against that criminal or the group that he is in as long as the following conditions are met:
- The criminal or his team is not considering another mission
- The criminal or his team is not on another mission
It is feasible that if you witness a crime and are not currently engaged in a mission yourself, you may be offered the very bounty that is generated. Generally, the instantaneous nature of the bounty mission offer when you perform your witnessing will tell you that you are being offered to engage that criminal.
Witnessing a player gives you petty cash and standing. (approximately $6APB and 1 organizational standing)
You can also arrest the witnessed player and all of other group members if present, just as in missions, by using Less Than Lethal (LTL) Weapons, which do stamina damage instead of health damage, allowing you to stun the criminal(s) and arrest them to gain more money and organizational standing.