I am looking to see if I have a civil case due to my mentor/best friend being shot from behind by the police.

I was not at the home when my best friend/mentor was shot by a police officer twice in the back inside his garage. I have became afraid of stuff that has affected my life. I spent everyday with him while his criminal case was going on due to him being depressed and us thinking he wouldn't win the suit the police put on him which he has won. I am now depressed, do not feel comfortable in public. I lost my will to want to be successful and don't feel I will ever be the same, I don't feel I am able to work, Everyday I wake up I feel I am going to have someone shoot me. I am depressed and the aniexty I am having is so severe I do not know day to day if I will feel good enough to get out of bed. Is this a possible civil case. I have my Federal Firearms license and now I will not shoot a gun and my gun shop I was starting is never going to happen since guns are now something I get nervous around and I shot competively my whole life, it was my only hobby now I hate it