I'm not an LEO (and I don't play one on TV), but you might do a google search of people that have received the death penalty (or are supposed to) over the past 5-10 years. Here are a few examples of human filth that come to mind:
Timothy McVeigh
Tookie Williams
John Wayne Gaycie
Gary Gilmore
Charles Manson
Sirhan Sirhan
James Earl Ray
Andrea Yates (bitch in Houston that drowned her 5 kids)
Susan Smith (bitch in South Carolina that drowned her 2 kids and lied about it)
Scott Peterson
OJ Simpson
David Burkowitz (Son of Sam)
Ted Kazinski (The Unabomber)
Jeffrey Dahmer
Robert Reid (The would-be shoe bomber)
The 19 9/11 Hijackers
Colin Ferguson (asshole that shot people on the NY subway)
John Couey (the piece of shit that raped and murdered 9-year-old Jessica Lunsford)
David ???? (asshole that kidnapped Elizabeth Smart)
Asshole in Idaho that killed those folks, including kid named Dillion, but did not kill his sister, Shasta
Asshole in Atlanta that grabbed the bailiff's gun and went on a shooting rampage, only to surrender to woman that read a book to him
The BTK killer (don't remember asshole's name)
How's that for a start?