There has been a bombshell revelation about the late Anna Nicole Smith!   Before her untimely death from a drug overdose, the she was investigated for plotting murder.

Just-released FBI documents reveal that the eccentric star was examined in 2000 and 2001 in a murder-for-hire scheme.  The alleged target was Pierce Marshall, the son of Anna Nicole's much-older oil-tycoon husband Howard Marshall.

At the time of the murder investigation, Anna Nicole was embroiled in a bitter legal battle with Pierce for his late father's $400 million estate.

Anna Nicole was questioned by agents about the murder plot on July 3, 2000, and according to the documents, "Smith began crying and denied ever making such plans."

The FBI documents say a revolver and 3.5-inch stainless steel knife were confiscated from Anna Nicole's home, along with a black and orange hat described as a "Dr. Seuss" hat.  The three items were returned to Anna Nicole seven months later.
 
Anna Nicole's sister Donna Hogan tells INSIDE EDITION, though she loves her late sister, the claims of a murder plot "wouldn't shock or surprise" her.

Other sources close to Anna Nicole tell INSIDE EDITION the whole story came from her ex-boyfriend Mark Hatten.  In 2003, while serving time in prison for making criminal threats against Anna Nicole, Hatten told INSIDE EDITION,

"She wanted me to take care of it for her...If I wasn't going to do it personally, to get a contract going to kill Pierce Marshall."

"So Anna Nicole asked you to kill the son of her ex-husband?"

"Absolutely, numerous times," he said.  "She'd get jacked up on pain pills and then this would come out and she'd start saying Mark you gotta kill him, I'm Anna Nicole I can't do it, you gotta take care of this for me.  I'll do anything for you, we'll be set.' " 

But according to a letter in Anna Nicole's file from April 2001 the FBI "determined that there is insufficient evidence to establish that there was a murder-for-hire plot by Ms. Smith to kill Pierce Marshall," officially closing the case.

100 pages of Anna Nicole's FBI files were released, and they're said to be only a fraction of what's in her file.