From
Kampfflieger Vol. 4 (Classic Publications):
The Luftwaffe had shadowed them to their destinations and that night a force of He 111s from KG 4 (whose I. Gruppe was to mark the targets), KG 27, KG 53 and KG 55 set off to catch the Boeings on the ground.
It's a while since I wrote that, so I can't now remember if I had more detail to base it on.