I had front row seats for a car accident a while back. It was dark, rainy and cold and I wanted to go home, so I didn't stick around or give my info to anyone. I didn't even bother to get the license plates or makes/models of the vehicles. I sent a witness account by e-mail to ICBC when I got home and described what the two vehicles looked like, approximately.
The vehicle in front of me had been waiting behind a left-turning sedan. At that point, he was entirely in the intersection already. Because of pedestrians and other vehicles running the amber light, the left turner couldn't turn until the light was already red.
This left him right in the middle of the intersection and needing to go straight through on his red.
Cross traffic started moving though. One car zipped around and in front of him, while most of the other traffic was hesitating, not sure what to do with him being in a weird spot. But then a taxi rammed right into his passenger side.
He was in the middle of an intersection on his red, so without a witness, I think he would have been completely at fault. They thanked me profusely for it and said they'd pay it forward. =)
I wasn't thinking about fault or liability at the time though. I wasn't sure who I would help with my statement, but I felt that independent facts should be added, just in case.