Here is an investigation by Dutch police of a 1995 cold case in which they are inviting outside participation, with a reward offered:

http://www.politieonderzoeken.nl/gerwig-engels/gerwig.html

Also, here is the website for Victoria (Australia) Crime Stoppers, inviting assistance with solving crimes and finding fugitives:

http://www.vic.crimestoppers.com.au

Here is an interesting article on CNN about how the Internet was used to solve an old mystery:

Amateur sleuths keep cold cases alive 

AB — originally posted 15 May 2007