Abandoned Robins nest

Hello. Last year we had two successful episodes of robins nesting in a nest box high on our garage wall. This year we had another pair who we observed coming back and forth building the nest, male feeding female etc. About 2 weeks ago this all stopped and it appeared the nest had been abandoned. The robins disappeared from the garden and only this week we have seen one Robin feeding in the garden. This morning, we noticed 3 starlings taking a keen interest in the nest box so we climbed up a ladder to sadly find 5 dead Robin chicks. They were obviously a few days old as they had downy feathers. I am curious to find out why the chicks were abandoned. I suspect that one of the pair of adult robins was killed, there are a lot of cats in the area. Does anyone know of any other reason? Thank you.