Possible knowledge skills (with possible contacts):
-investigation techniques (detective; police or PI)
-forensic science (coroner, crime scene tech)
-criminal psychology (detective, federal agent, criminal profiler, psychologist)
-psychology (duh *grin*)
-sociology (university professor, grad student)
-police procedures (patrol officer, detective)
-criminal law (district attourney, lawyer)
-criminal syndicates/most wanted lists (criminal of choice, federal agent/police from appropriate task force, bounty hunter)
-gangs (police, gang member)
-music (Holmes liked to play the Violin if memory serves)
-illegal substances (gamg member, gang lieutenant, drug dealer, federal agent/police officer)
-black market operations (black market member, federal agent)
Note: federal agent/police can be swaped with corporate counterpart.
Just a few off the top of my head.