Free an imprisoned slave

Go to The Mayor's Office in Vacherie

• from room The Ohio River (with s exit): 4sw3swse2s2w
• or go along the Mississippi until you find On the Mississippi, by a Small Village and head 2s2w

ask Mayor slave
ask Mayor pardon

(you can skip the above when repeating, and maybe on the first one too)

go to The Master's Office on the nearby plantation

• From Mayor: 2e2nesenn, open n, nnue

From here you can do the following to get a pardon letter

• ask the master about the pardon, then pay them 20000 coins
• Kill them

Either way, take the pardon letter back and give letter mayor. The slave is freed and you get xp.

There is some kind of cooldown on this, so sometimes turning in the letter won't give you xp, but it is infinitely repeatable.