Can an employer fire me for soemthing that supposedly happened 2 months prior?

I was fired for my job 2 months after i supposedly done something. This girl i worked with got fired, called back in and said that i had threatened her back in January. This took place the first week of March. They suspended me for one and half months. They called me back in after doing their investigation, and supposedly 2 managers heard me say it, in January. So if they really heard me say it in January shouldn't I have been disciplined in January? Im so confused and i could really use some help. I have tried to get copies of the staement wrote agaisnt me and they will not allow me to have them. What should i do?