His educational background has been called into question because nobody remembers him at MIT and his transcripts don't exist there, but investigation since his initial claims have found phonebooks showing him at Los Alamos, and a contractor there identified him as an employee. This was Stanton Friedman's biggest gripe. His birth records have also been wiped.
Furthermore, when discussing his background check to work at A51/S4 he stated to Noory that he checked by the FBI. Subsequent research found the agency used by A51 was "OFI" -- phonetically similar to "FBI", but it indeed was the company that did the checks.
Then there is Element 115, which Lazar spoke of in 1989 and was only synthesized in 2003 (an unstable isotope of 115).
Definitely not thoroughly debunked.
LOL, I used to fall to sleep all the time listening to Art Bell so I've got all of this memorized pretty well :)