A Chappaqua school was forced to enter into a precautionary lockout on Tuesday morning, as local and county law enforcement conducted a search in the community for a man suspected of larceny in White Plains. Between 9:15 and 10:15 a.m. on Tuesday, Robert E. Bell Middle School entered a lockout mode, according to Principal Martin Fitzgerald, which included keeping students inside and securing all entrances to the building as a precaution.