An officer on guard over the captives in Assassin's Creed III

The captives are natives held before being auctioned off. There are at least 4 in each of the 3 sets Haytham Kenway needs to free from Southgate Fort. There can be as many as 6, but Haytham only have to free one pair to set the rest free as well. There is always an Officer around for you to deal with.