Yep, this solution does not take into account that the killer should have seen all the dead people that day. So the tests are written incorrectly. And the spread operator in this context is just an overcode, you can write dead[0] and the solution will still pass the tests.

I see, if the example in the description would have Johnny as the first value, it would fail.

You're right. The problem is in includes(...dead), which only checks the first name in the dead list. The current test cases likely miss this bug and should be updated.

Because it works, why do you say it shouldn't?

This solution should not work for this problem, I don't understand why it is among the correct solutions.