Two women rescued a child who was kidnapped by his neighbour.
or
Two women rescued a child who had been kidnapped by his neighbour.
Which one is correct and why?
Two women rescued a child who was kidnapped by his neighbour.
or
Two women rescued a child who had been kidnapped by his neighbour.
Which one is correct and why?
Two women rescued a child who had been kidnapped by his neighbour
The action in the independent clause is set in the past and it's over (rescued, past simple). The kidnap happened before the rescue, so you use a past perfect (had been kidnapped).