Timing Bobby after making a bet that he can't get a girl's number at the bar in a certain amount of time. (an early clue to him being the killer)
Numbers drawn in Rafe's blood, left by Lucas to hint towards using a black light on the back of everyone's jackets.
Letters written in fluorescent powder, left by Lucas on the jackets of everyone to spell out the word "Croatan".
Being told by Sara that she trapped the killer by messing with the clock in the break room and putting fluorescent powder on it, knowing the killer wouldn't be able to resist setting it to the correct time.
"But at the end of the day, building a better mouse trap is just... pure mechanics. It's knowing how to bait a particular mouse, that's the fun part."
"So, there I was sitting next to the bodies of my parents just waiting for someone to ask me why I killed them, you know. And this detective comes up to me, right? And he says: 'Want some gum?'"
"Gum... No one asks, it never even occurs to them. And like after every first high, it's harder and harder to get to that place."
"Then, you finally get so good, there's no feeling at all. It's easy. Finding a worthy prey, a challenge... That's hard."
"So, while you were studying tired old hacks like Bundy, Gacy, Dahmer, I was studying you. Your habits, your hangouts, your weaknesses. It was so simple to set you all on edge. I had to push here, pull there, but once I did, I knew each of you would play your part."
"The key to effective illusion is misdirection. All I needed was opportunity. The coffee break gave me the chance I needed to rig a few little surprises."
"Go ahead, Sara. Arrest me. We have your blood under Rafe's fingernails, your fingerprints on the fire extinguisher, and your bullet in my neck. It don't look good. You're f-cked."