Personally I think Bob Lazar is full of ***. He has brought no evidence to the public about his stories, but just the words he speaks.
As the "work he did at area 51" would have been classified, and still would be today.. the government would not need to kill him or discredit him secretly at all. Instead, they could enforce the punishment on the disclosure he would have signed when working there which would probably be death or jail for life. They wouldn't need to fart about with a conspiracy to get rid of him as they would have the right to punish him legally.
They're not stupid.. I don't really believe the US (whatever your thoughts about them might be) would actually let some nerdy guy called Bob walk around the streets telling everyone what he did at one of (if not the most) secure placements on the planet and it would be foolish to think so.
Peronsal thoughts..
I think Groom Lake is home to some of the most advanced air combat / spy / transport technoligy today, along with weapons far more advanced than what you could really think about.
Alien count on the other hand.. none.
Maybe they have parts of metal alloys etc that can't be placed to anything on earth, or matter which is of alien origin.. but I don't think for a second they have a big saucer sitting the basement having lots of white coats dismantle it.
;)

You got a good point Euro, it seems that almost all good things can be found in america if you ask these americans, as if its heaven....

well said mike, i definitely would rather join usa than euro any day, im also a scot, definitely flying discs and more there, watch dreamland even though its hard to find.there are others, highly educated people, who claim to have worked with aliens at groom lake @ s4.

There are no aliens visiting earth,distance to far,nearest star 4 light years.
Warping (bend) space is a theory.Secrets is only knowledge that people keep to themselves all over the world,it's only people that are nosey and want to know others business,so call them secrets.I'm Scots and not European,I'd rather be referred to as an American in waiting than a Eurofile any day.

oh you americans and your "secrets". As everything else in the US is like they'd be just next to a god. So. If aliens visit earth it's the americans that own their technology and secrets.. And hey. This documentary could be fraud also? America is not as meaningful thing on earth as americans thinks..