Shahidul Ahmed, 41, was put on trial after DNA evidence linking him to Rachel Manning's death was discovered following his arrest for an unrelated matter in 2010.
He hit Miss Manning repeatedly with a steering lock after she was dead, causing broken bones, Luton Crown Court heard.
DNA found on the steering lock matched Bangladesh-born Ahmed after it was discovered by the road on the direct route between the spot where the body was hidden and Shahidul Ahmed's home.
More top news
Mack entered her plea in federal court in Brooklyn. The judge refused a request by her lawyers to release her without bail.
Officers investigating a reported break-in on Friday found 22-year-old Roger Alvarado asleep in the pop star's home in Tribeca.
Billy Jeeves is said to have fled the scene in Hither Green, south-east London, after Henry Vincent was fatally stabbed by the pensioner.