Not been put in that position, closest is when I witnessed a crime while working.
A big retail estate somewhere near Birmingham, they had problems of theft from cars, ie. broken windows and radios etc. stolen from within the vehicle. The management of the estate wanted it protected and I was asked to come along and show how CCTV could be used.
I got one of my team to bring along the CCTV demo truck and parked it up in a likely position in the carpark, set up the cameras and waited for the client to show up, the salesmen from the local office arrived and just before the client was due a red car came speeding in to the carpark and not 50m from where I was sitting stopped beside a BMW, then a guy got out the passenger side of the red car with a hammer, broke the window of the BMW, he leaned in and in seconds extricated himself from the window with the BMW's radio etc. hanging from his other hand, he jumped in the red car's passenger seat and it sped off.
I got it on tape, I got the registration number of the red car, the salesmen seen it all happen, but none of them wanted anything to do with it, I reported it to the police, they got the tape and all the details I could give.
3months later I got a call from the police to say they had caught the guy and asked if I would come to an ID parade.
I had to take a day off work catch the train - I got 1st class travel from Newcastle to Birmingham went to the police station and the suspect was a no show.
Later the police told me that very few people actually will go to an ID parade or even act as a witness and that the suspect did not expect me to show up. Later he was arrested and confessed, it went to court and along with a few other things he had done, he got 3 months jail.
I was really quite shocked at my colleagues, we are supposed to be a security company and they did not step up and be counted.
Oh, we did get the job to secure the whole estate not just the carpark