How can I disconnect power to an ADT alarm system?

I recently bought a house where the previous owner had an ADT alarm system. Since home alarms are next to useless, I didn’t continue the service. Recently, I had a power outage due to hurricane Matthew. I left the house and came home a few hours later to the alarm system beeping like crazy. It had to go.

I removed the keypad with no issues. I unscrewed everything in the control box and removed it. Unfortunately, nothing was labeled. There are eight sets of 22/4 wires (not 100% sure on gauge, but it doesn’t matter). I’m sure one set went to the keypad, one set to the motion sensor, one set to the front door. But that leaves, 5 sets for… who knows? Obviously, one is for power. While removing the control box, a red and black touched and I saw a small spark. Its getting power from somewhere. Where do I look to disconnect the power?