Rico wrote:Well if the person is next to you and dies, you should be able to tell what killed him from visual effects and sounds.
e.g a heavy machine gun will rain a lot of bullets on your position, where as a sniper shot will be in short loud bursts. And im sure you will know when a tank shell goes off

Should be interesting
Most of what you say is sort of true, it depends on the situation.
The sniper part, however, is wrong. If you're in a battle chances are that any sniper shot will drown in the other battlesounds. If it's "quiet" and the sniper is a good one, he/she is so far from you that all you would hear would be the bullet hitting your partner.
Assuming that the speed of sound is approximately 1116 ft/s and the sniper is at least 400 yards away it will take over a second before you hear the report of the rifle. And considering the muzzlevelocity of the rifle being around 2800 ft/s the bullet will arrive on target in about half a second.
The muzzlevelocity figure is not generic by the way and differs greatly depending on the weapon and ammunition used. The 2800 ft/s number is for the M24 sniperrifle currently in service in the US army and marines. (Marine designation M40A1.)