In a previous post, I talked about how Random Numbers are actually not so random and depend on many external factors.
Based on that formula, we could come up with a pattern and a relation between the random numbers selected by Serial Killers. Then plug this formula into suspects to rule them out.
Lets take 100 serial killer, and let each choose a number between 1 and 10,000. Chart out the results against their birthdays. Then use Fourear series and quantum mechanics to approximate a formula that will let you limit the numbers range. The resulted chart will be interesting. You may change the variables or add more and see the result.
Now, to test out if someone is a serial killer you only need to plug in his birthday and let him select a random number, if his result fell near the drive of the function. Then most probably your guy is a serial killer.
That's Nuts I know. But hey I'm thinking loudly. Others have listed the serial killers characteristics already.