The Disappearance of Danielle Imbo

On February 19th of 2005, Danielle Imbo and Richard Petrone disappeared after leaving a restaurant in Philadelphia. Danielle has been separated from her husband while Richard was her "on-again, off-again" boyfriend. Danielle had a young son while Richard had a teenage daughter. Richard had exchanged threats with Danielle's ex-husband before while Danielle herself wanted "space" from both of them. The FBI entered the investigation in 2008 and the case remains unsolved. But what happened that night? Was this a murder-for-hire? If so, by whom?