In the early hours of Monday morning, he began tearing up the prison - smashing windows and and destroying the ground below.
The murderer was in a tense stand-off with riot officers on Tuesday. Two officers with shields were seen making their way up a ladder in the roof space close to where the prisoner was holding his protest.
As they made their way onto the roof Horner was seen walking towards them with a metal rod in each hand.
The police advanced him after he had continued to cause damage to the building kicking off CCTV cameras and smashing windows.
A 'party protest' began outside on Monday evening, as crowds gathered to show their support for the convicted killer.
Horner was arrested and handcuffed as he descended from the roof, with his arms raised aloft in celebration.
Seconds before he finally finished his protest, Horner shouted: "I've proved my point. I've got a 12 inch pizza and a can of coke.
"I've done what I wanted. I've had a mad one."