When the ancient mariner killed the albatross the sailors were angry because they believed the bird brought the wind, but when the mist disapeared they changed their mind because they now thought the bird had brought the mist. "T'was right, said they, such birds to slay, / That bring the fog and mist."
But soon the sailors realize that they are cursed and everything goes wrong; the ship stops, the heat becomes unbearable, there is nothing to drink and there are many horrors at night. The sailors and the mariner knew this was the consequence of killing the albatross and the sailors were very mad at the mariner.
To punish the mariner the sailors put the carcass of the dead albatross around the mariners neck to signify his crime and place the guilt on him and him alone.