If you found 12 evidence pieces you're doing well for yourself! :) :) :)
A couple of hints (scroll down for spoilers -- please tell me if you know how to use a spoiler tag in this chat):
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Are you calling people on the phone? The priest at St. Michael's is worth talking to. You can find his number by looking for "St. Michael's parish" in the Herald's search engine.
Some of the people who took part in the case are still alive.
There are 30 pieces of evidence, but you do not need them all to solve the case.
Feel free to ask for more if you already knew these. :)