The Philly Inquirer has a really interesting story about the murder of Betsy Aardsma, a student who was fatally stabbed in Penn State's campus library almost 40 years ago. The case has never been solved, but it's attracted the attention of several amateur sleuths. One of them built a Web site about the case, whokilledbetsy.com. The amateurs have actually helped push the authorities to take a new look at the murder.
Here's a magazine article about the Aardsma murder.
Hat Tip: Many thanks, goshel!