Take one person, one room and one weapon and place them in an envelope where nobody can see them. Distribute the other cards out between the teams randomly. The teams of 2 or 3 must guess who the murderer is, where they murdered and with what weapon.
Teams take turns to ask questions to the other teams, during which everyone else can collect evidence and eliminate potential suspects, weapons etc...
However, they can't ask a direct question, ie. What cards do you have? Is it Professor Plum? Do you have a knife? This forces students to cask indirect questions such as "Do you have the man who works in a hospital?".
Each team gets one chance to make a guess at who/what/where and can do so at any time. If they are correct then they win the game, otherwise they are out but they carry on answering questions for the other teams until somebody guesses correctly or all teams are out.