Law enforcement officials are tightening security in and around the nation’s prisons, high schools and colleges, and have issued special advisory warnings to celebrities and politicians as millions of loners, many of whom they fear may be prone to violence, join the literary community and the rest of the nation in mourning the passing of J.D. Salinger, the reclusive author of “Catcher in the Rye”, who passed away yesterday at the age of 91.