It sounds like they are in possession of some correspondence of his, but it's not really clear right now. They have been investigating this lead since before Patsy died, so I would think they have lots more than a hunch.
Apparently there's quite a package of email correspondence he conducted with a CO professor who became suspicious about him and tried to string him along, trying to get more info, for quite awhile:
http://www.rockymountainnews.com/drmn/local/article/0,1299,DRMN_15_4923202,00.html
They are being quite reticent with the details so far, but "hundreds" of emails exchanged with the prof would seem to indicate quite an obsession with the matter.