"4 NM from the threshold" it definitely was not as the distance to the sea is at least 7 NM. Would have been easy to check.
If they were indeed descending through FL 120 and cleared for 4000 feet for an ILS approach, but were observed to be at roughly 1000 ft some 10 NM out, this would suggest to me their problems had already started a bit earlier and they could not control the descent for some reason. Hope for answers soon.