Feds eyed busty blonde for her part in a murder plot to kill tycoon hubby's son.

In 2007 the FBI dropped the probe for lack of evidence before Anna Nicole Smith died form a drug overdose.

In a stack of voluminous files obtained by Associated Press under the Freedom of Information  reveal that agents investigated the buxom party girl in 2000 and 2001 in a murder-for-hire plot against E. Pierce Marshall.

Smith married the 89 year oil millionaire in 1994 when she was a topless dancer at age 26.

The younger Marshall battled for years in the legal system in a bid to keep the Playmate from collecting her inheritance on his father's oil fortune estimated worth in the millions.

Marshall the Younger died in 2006 from seemingly natural causes.

Whole chunks of Smith's file are whited out after agents found no probably cause.

"Smith adamantly denied ever contemplating such a crime," an agent wrote and that she "began crying and denied ever making such plans."

Assistant U.S. Attorney Sally Meloch finally wrote the FBI on April 26, 2001 she had "determined that there is insufficient evidence to establish that there was a murder-for-hire plot by Ms. Smith to kill Pierce Marshall."