I'm not sure if this is hacking, some sort of glitch, or an exploit, but it's definitely reportable. So a player named "TheRubberFruitFace" joined, then, in office (at around 8:30 EST) some people were hanging around and they were suddenly killed, by said player. The next map, vsh_dr_mario_b3, he did the same. At around the middle of the map, he began shooting at me. He also appeared as a ghost. I have a screenshot of him alive and on the activators team. Note that there are 2 people alive. (The other person on activators has nothing to do with this, he's innocent.)
Here's a link to his profile. It's private, but it was required.
http://steamcommunity.com/profiles/76561198136391192 Steam ID: STEAM_0:0:88062732