The Usual Suspects

Here's an interesting logic puzzle whose solution isn't at first obvious.  Six suspects in a bank raid, all blaming each other.  But is there a way to deduce from their lies and half truths who actually did it?

The Usual Suspects have been brought in after a bank raid.  All of them have previous records and may well have carried out the raid.  They are also notorious for trying to stitch up each other to take the blame.

From CCTV footage, all that's known is that there were two robbers.  The CCTV footage is grainy and poor quality, and so that's all that can be said for certain.

So the police bring them all in for individual questioning.

  • Andy is certain he knows who did it - it was Charlie and Barry.
  • Ernie is equally certain - it was Donald and Frank.
  • Donald on the other hand puts the crime squarely on the shoulders of Frank and Charlie.
  • Barry, the oldest and gnarliest of the bunch, spits out the names Andy and Charlie.
  • Charlie seems unfazed when he's told that his name has come up most often.  He calmly denies the charge, and places the blame on Donald and Ernie.
  • However, when it came to questioning the last suspect, Frank, he pleads his right to remain silent.  He says nothing.

The detectives carrying out the investigation were flumuxed, until one hit on a thought.  He was pretty sure they all knew who did it.  But as well as staying out of prison, each was also trying to save his own hide by avoiding being a snitch.  Therefore:

  • If any one of them correctly named the two perpetrators, their would be retribution amongst the criminal class and they may end up dead.
  • If any one of them named two innocent perpetrators, then the case would fall through and would still be open.  They'd still be at risk of going to jail.
  • But if each named one guilt man, and one innocent man, the case would likely succeed, and they'd likely avoid retribution.

Therefore, this wily cop thought, on balance it's likely that each many has given the name of one innocent man, and one guilty man.

"I've got it!" the detective cried out, spilling his coffee. "I know who did it!"

And as it happens, he was right.

So, who did it?

If you're feeling logical, stick your thoughts down in the comments first, before checking out the solution.


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