This page details many of the offical facts of the case recorded by the FBI. It provides a good overview of what we know without going into the many theories of what really happened
This news article contains information from amatuer sleuth Eric Ulis, who has been analyzing Cooper's tie for many years. He feels strongly that the particles he has found will give us the answers we seek.
This article from Historklink.org details the finding of Cooper's cash along the Columbia River.
This is the offical FBI report on Mccoy. It does not directly mention the Cooper case since Mccoy was cleared as a suspect, but if you want to understand why people think it might have been him, this is a good place to start.