Mankato (KMKO)-An undercover drug purchase in Mankato yesterday led to the arrest of a man on crack cocaine charges.  Several law enforcement agencies coordinated the purchase from Donny Emery Lee Lawson, who then led officers on a chase.  Some of the items he threw from his vehicle during the pursuit were found to be crack cocaine and he was taken into custody.  Lawson is being held in the Blue Earth County jail and faces several felony counts, including controlled substance violations, fleeing in a motor vehicle and second degree assault.