Canon Background
https://awoiaf.westeros.org/index.php/Cotter_Pyke

In-Campaign
Cotter met Ser Darron, Ser Carsen, Jardon, and Thomas at the docks of Eastwatch as they made their way North in the later part of 283 AC. Under the shadow of The Wall he greeted the travelers brusquely and let it be known that they could purchase supplies from his quartermaster. Before parting ways Cotter warned that if they were traveling beyond The Wall to sell arms to the Wildlings that the crime was punishable by death.

When the southbound vessel chartered by Darron, Carsen, and Jardon sought shelter from an easterly storm at Eastwatch’s harbor Cotter met the vessel on the pier with a contingent of black brothers. At first he was most concerned with the presence of Yris and her snowbear… until one of his men discovered the clothing of a sworn brother of ‘the watch’ in a cabin onboard. Cotter began to interrogate the men and called for the headsman’s block and his ax. Meanwhile the trio offered variances on the story that they had indeed encountered Arthur but had executed him and meant to return his garb to the Night’s Watch. In response Cotter voiced concern over the fates of the two rangers who had been traveling in Arthur’s company at the time of his disappearance. Ultimately, Jardon cracked under the pressure and revealed that the truth… that they had knowingly aided Arthur in breaking his vows. After some consideration Cotter declared that he would not execute the men as they had not broken their own vows, but ordered that they pay restitution. Ser Carsen suggested they turn over Thomas’s care to the Night’s Watch but Ser Darron forbade it. Instead each man was ordered to pay a 100gd penalty, as the watch needs coin just as they need men. Ser Darron and Ser Carson paid the coin from their own purses and covered Jardon’s atonement as well.