Lil Wayne has turned to a former FBI weapons expert to help prove his innocence on gun charges dating back to 2007.

The rapper is facing two second degree felony counts of criminal possession of a weapon after a police search of his tour bus during a stop in New York turned up a .40 Caliber handgun.

The Lollipop hit-maker has pleaded not guilty to the allegations, with his lawyers maintaining the arresting officer conducted the search illegally after claiming she smelled marijuana wafting from the bus in July 2007.

Wayne - real name Dwayne Carter, Jr. - insists the gun is registered to his manager Cortez Bryant, making it legal, and is challenging the method used by authorities to gain the DNA results which they claim connect him to the firearm.

And according to the New York Post, Wayne has hired ex-FBI geneticist Bruce Budowle to prove the cops' results wrong and help him avoid prosecution.

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(This news article provided by World Entertainment News Network)