AceShowbiz - Oksana Grigorieva will struggle to fight allegations she secretly taped phone calls with Mel Gibson with the purpose of extortion - her former bodyguard insists she wanted to "pressure" the star into handing over a financial settlement. The former couple split last year and is currently locked in a bitter custody battle over baby daughter Lucia.

The break-up turned nasty when Grigorieva accused the actor of domestic violence, and captured him on tape allegedly confessing to striking her. But police have been called in to investigate the Russian singer amid claims she purposely recorded the heated phone conversations with Gibson in a bid to force him to pay her a settlement sum to keep their disputes out of the press.

Grigorieva has denied the accusations, insisting she only taped Gibson's angry calls because she feared for her life - but her former security guard Kristian Herzog claims otherwise. Herzog, who was fired by the singer in October 2010, tells TMZ.com she wanted "to pressure Mel to pay her money" and suggests Grigorieva plotted the extortion early on, branding her a "sexual sorceress".

He has also defended Gibson against allegations he punched his ex - he claims Grigorieva told him all about the violent incident and admitted that the actor had only slapped her.