Murder or Self-Defence?

When I was 16 I killed a man, I was pretty shure he was out to get me. I was put in a situation far away from home that I was not able to deal with. It later turned out that the guy I pushed out the window was a either KGB or RGU not shure. I have not told another living person about this and it has been very heavy on me for years. I am sorry I did this but I saw no other solution at the time and still do not looking back on the situation. The whole deal was coloured bad from the getgo. I am Sorry.