The dumper was later found abandoned and the driver had fled, police said.
Constable Mahavir Singh flagged the dumper to stop at Palla outpost at around 3:30 am today, but the driver, who was in a tearing hurry, crushed the constable to death killing him on the spot.
The killer driver then rammed the dumper into a Maruti car, before abandoning the vehicle at Badarpur on Delhi border.
Police suspect the dumper was being used for illegal sand mining by the local mafia.