After the horrors of the Virginia Tech massacre, a popular game on campuses nationwide called “Assassin” is raising concerns and prompting warnings from police. Officers in three communities in Illinois and Pennsylvania urged students to halt the games, which involve ambushing other players with sometimes realistic-looking toy guns or other objects, after the Virginia Tech shooting last week that left 33 people dead. Police say they worry that players, mostly college and high school students, would be mistaken for real-life killers, endangering themselves and others.