Using an eight-station time of arrival (TOA) network composed of NaI(Tl) scintillation detectors and wideband electric field derivative (dE/dt) antennas covering approximately 1 km² on the ground, we have located both the sources of X-ray emissions and electric field changes produced during the leader phase of both downward negative natural and rocket-triggered lightning strokes. We show that the sources of X rays and leader step electric field changes are co-located in space within 50 m and that the located X rays are emitted 0.1 to 1.3 μs after the origin of the leader step electric field changes.