Heh. I believe the quote is:
All mysteries are solvable, in fact there are always two ways to solve any single mystery, but player skill and a small amount of luck are necessary to nab the guilty suspect.
This would be that small amount of luck. Seriously, when you start a mystery with very few visible suspects, it's a good idea to first ask the "do you kno0w anybody with a motive" question. That way, you will most likely open up additional investigation routes before your only choice dies or clams up.