1.11. Two brothers are involved in a murder. Though
it’s clear that one of them actually committed the crime, neither can be
punished. (This is different from #1.78.) (from “Unreasonable Doubt,” by
Stanley Ellin)

1.11 answer: One of the brothers (A) confesses to the murder. At his
trial, his brother (B) is called as the only defense witness; B immediately
confesses, in graphic detail, to having committed the crime. The defense
lawyer refuses to have the trial stopped, and A is acquitted under the
“reasonable doubt” clause. Immediately afterward, B goes on trial for the
murder; A is called as the only defense witness and he confesses.
B is declared innocent; and though everyone knows that one of them
did it, how can they tell who? Further, neither can be convicted of perjury
until it’s decided which of them did it… I don’t know if that would
actually work under the US legal system, but someone else who heard the
story said that his father was on the jury for a very similar case
in New York some years ago. Mark Brader points out that the brothers might
be convicted of conspiracy to commit perjury or to obstruct justice, or
something of that kind.

1.11 variant answer: Scott Purdy says an L.A. Law episode
had a similar plot: A petty criminal and a mob boss were accused of
murdering someone. The lawyers offered to drop the charges on the criminal
if he’d testify against the boss. He said he would, got his charges
dropped, and confessed on the stand. Both got away without being punished:
the charges couldn’t be reinstated for the one, and there was reasonable
doubt for the other.