For this achievement, you need to put a number of items on the Guard Captain's body. His body is near the tavern, on the north side of the market. You need to do this in the market, before you move onto the estate. The items are:
- The 3 different items you steal from the shops in the market. DO NOT put them into other shop chests. If you accidentally put one in another shop chest, you can still take it out - but if you put all 3 in different chests, you can't get them back out and can't get the achievement.
- Bann Terrin's under garments. You fight him on the east side of the market. DO NOT put them on the Chantry Board, you can't get them back.
- Mages Collective Signet. (
This is the one item you don't actually have to put on his body, you can give it to Sketch instead if you like - still listing it for completion purposes). First you'll need to find all the markers. To start the quest, go to the spot where the Mages Guild bag is in the main game - just west of the chantry, or on the other side of the building that has armour shop in the main game. Then there are two markers - one is just west of the bag along the buildings, and the other is near where you started the DLC - go north up the alley from the main entrance to the market. Finally, go all the way west near the gate to the city elf slums (in the main game). Go near the sparkly spot and you'll get attacked, defeat the mage and take the ring from his body.
- Jovi's body - go past the Guard Captain and down the alley and you'll have to kill the guy near the doorway. You can then take his body.
Plant all these items then go signal Marjolaine. If you did it right she will say you did a fantastic job destroying his career, and you should get the achievement.
(Taken from my DLC walkthrough on gamefaqs.com -
http://www.gamefaqs.com/xbox360/998445-dragon-age-origins-le...)