Pierre Thomas -- I Watched Will Smith Die ... 'Over a F**king Fender Bender'

NFL running back Pierre Thomas says he'll be forever scarred after watching his close friend, Will Smith, get shot to death in New Orleans ... saying, "These images that I have in my head will never leave me."

Thomas was at the scene when Smith got into it with Cardell Hayes -- and says the whole thing erupted after a "f**king fender bender" ... not a revenge plot as some speculated.

Here's Pierre's post in its entirety:

"The last few days has been a whirlwind and I am still trying to wrap my head around this whole thing. I flew out of New Orleans last night and back to Chicago because I couldn't think straight... I witnessed a close friend, teammate and a man that I thought of as one of my big brothers in the NFL shot to death OVER A F**KING FENDER BENDER!!!!"

"Why!? I just don't get it... these images that I have in my head will never leave me and I understand that and will have to live with it."

"I want to thank each and everyone of you, my family, friends, fans and the entire Who Dat Nation for all of your thoughts and prayers.... But let's send them instead to Will's family- his wife and 3 kids who have to be strong during this difficult time."

"People!! When is this sh*t going to stop?"

"There is so much senseless killing going on in our world, and I'm not saying that I have the answers to fix it."

"But I am willing to do my part to help and find a solution. My heart is heavy and I wish I could turn back the hands of time, but what is done is done."