Why was Formula One's 1975 Grand Prix round in Spain stopped permanently mid race?

Question

Who, in 1955 and 1956, was the first British driver to win the Mille Miglia, the British Grand Prix at Aintree and the Monaco Grand Prix?

Answer 1

One of the cars crashed and then flew over a barrier killing 5 spectators
The track was a street circuit. The race continued for another four laps after the crash but was then stopped permanently, just over a third of the way through the scheduled length. It was the fourth, and last, Grand Prix to be held on that circuit. The driver broke several bones but was not hurt fatally.