( Contactmusic ) - BRITNEY SPEARS' close friend SAM LUTFI has been interrogated by KEVIN FEDERLINE's lawyers in a bid to reveal intimate details of the troubled star's life. Lutfi - who has been an integral part of Spears' world over the last few months - was ordered to give a deposition as part of the singer's ongoing custody battle with her ex-husband over the former couple's two sons. Mark Vincent Kaplan, acting on behalf of Federline, quizzed Lutfi on all aspects of Spears' life, including her activities at home and her relationship with her children, according to TMZ.com Lutfi was also asked about his links to celebrity photo agency X17 over claims he and Spears have been making money by tipping off the paparazzi - something which has been denied by the agency in question. Kaplan plans to use testimony from Spears and other key witnesses to convince Los Angeles Commissioner Scott Gordon that his client, Federline, should retain primary physical custody of Sean Preston, two, and Jayden James, one. Spears has been stripped of all custody and visitation rights following a string of ill-advised incidents. A custody trial is set for April (08).