Why is the FBI closing the anthrax case without investigating Philip Zach, the suspect who stole the anthrax?

Question

Why didn't the FBI want to investigate Dr. Philip Zach, a Jewish microbiologist that was CAUGHT ON VIDEO SURVEILLANCE CAMERA stealing the anthrax spores from Ft. Detrick.

http://en.wikipedia.org/wiki/Philip_Zack

http://www.anthraxinvestigation.com/hcourant.html

http://www.informationliberation.com/index.php?id=16283

Answer 1

Are you kidding, they have a guy that commits suicide, they figure the case is now closed. I mean, come on, why should they actually do their job and continue to investigate?  

Answer 2

Because the government is in on it so they don't care

Answer 3

Because further investigation would probably reveal information that is too sensitive for the American people to know.

Answer 4

Yeah there was no conspiracy. They only had the guy on camera stealing things from the lab. Case closed so much for America's credibility.

Answer 5

Same with Oswald, dead men tell no tales. Case closed.