What to do when person claims truck sold improperly and wants it back?

Neighbor was selling his son's truck. Son was in jail. Father had signed title. Dmv processed title.All this about year and half ago. Son now out of jail and calling police saying father wasn't supposed to sell truck. I am correctional officer (son was inmate in different institution than one I am at). Son is paroled felon. Could be retalitory? Chance of son getting truck back and us being out thousands of dollars. Father also sold several other vehicles belonging to son but son has made no complaints about them.