2009 Pontiac g6

My car stalled on me a few months ago and was diagnosed as needing a fuel pump replaced. I got it replaced and it still didn’t start, so I thought maybe my battery was bad. I took it to a different place and they said my engine was seized! I took it then to a friend of mine who works with a mechanic, they opened the engine and found pellets from a pellet gun inside the engine. How is this possible, and should I suspect my car was tampered with? Will my engine be ruined? I am worried I know who did this what should I do?