Russia won’t rehabilitate officers executed in Katyn
Note that Fantastical Melancholy already featured a lengthy entry about Katyń once in the past.
Some other sites to explore:
Polish government page on Katyn (in English)
Katyn massacre on English Wikipedia (looks quite well researched)
Zbrodnia katyńska on Polish Wikipedia (more photos from the exhumation)
Polish Institute of National Remembrance (don’t ask me, I didn’t translate the name)
Katyn Museum web page
If you want more, there are even more links here (haven’t had the time to thoroughly go through that site but it looks quite interesting itself, if slightly underfunded in the graphics design department).