In 102(a) it says that if you published the material before he invented it, then his patent is invalid. This is also problematic, because it involves determining when he came up with the invention. However, if he didn't really invent it, he'll have a hard time coming up with proof that he invented it before the publication came out.
Yes, materials published many years before a filing priority date would be considered useable as prior art. The U.S. has a quasi-grace period of a year for things published by the inventor him/herself, but for the time frames you are taking about it wouldn't matter if the publications were by the inventor or by others.
Since March 16 2013 the US is now a first to file country. It is no longer relevant when the inventor invented - only when he filed. For application filed before that date, something published before filing would be sited as prior art by the examiner and it would be up to the inventor to "swear behind" the purported prior art publication dates and otherwise establish that the actual invention occurred before the publications.
If the application is in a particular early stage of examination, any third party (you) can submit material to the examiner using a third party submission process created by the AIA. There is no or very little fee associated with this. If a patent has issued, the information could be used in an IPR preceding (also from the AIA) to try to get the patent invalidated. IPR is much less expensive than an actual courtroom action but still in the $100,000's of dollars - mostly for attorney fees. The USPTO fees start at $15,000.