By now fortunato has drank enough to be drunk he even showed it in his gait. So he was to drunk to gain suspicion on the trowel around montressors belt, so he just asked him if he was a masson.
LET ME OUT!!!
As Montressor lead Fortunato down the catacombs, he took him into a room where he could begin his plan...
Montressor then chained Fortunato to the to the wall precluding his escape of the catacombs and Montressor began to taunt Fortunato as he struggled. Struggling just made his cough worse because of all the niter on the wall
Feeling accomplished for what he did Montressor walked out of the room and began to cover it up with stone while Fortunato begged in the background to be let out
As Montressor started to build the wall he was hesitant to continue to build the wall and he even stopped and sat on the ground to decide if he wanted to keep going but he stayed true to the plat and finished the wall.
When he finally finished the wall he walked away he had impunity, no one ever found out and never found what happened to Fortunato. Montressor finally got his retribution.