How do I get charged with battery with a deadly weapon if my friends did it?

I was walking out of a bar and got into an argument outside and got hit with pipe. My buddies ran out and beat him with it. All the while, I was out cold. Next thing I know, I'm down the road and cops behind me and take us in. They took pictures of my head and face from me falling on it. A year later, I and 2 others get charged with the same things, 2 battery with a deadly weapon and attempted battery. I told the cops what happen to me and they obviously didn't believe. Why am I getting charged when they even took pictures of my head and face and knowing I didn't have anything?