Not sure if this is really needed since everything is marked on the map for you but in case you are not aware of those markings or didn’t read the mail they sent you hopefully this helps.
Prequisites
- You must have completed Hard Boiled (and Ceremony and Alimony) first. Hard Boiled is completed by visiting The Dead End in Eastern Commons Section of Divinity’s Reach.
- Return to Lion’s Arch after and talk to Inspector Kiel in Grand Piazaa, she will port you inside a story instance called Scene of the Crime.
- Talking to Marjory Delqua will grant you a Tassi Box with a #1 ability that you will need to use on the marked NPCs. If you have fast ground targeting on, you will need to stand on top of the NPCs and target them to use it.
June 19
- Only 3 suspects can be acquired today: Vorrk, Morraloo, Kasparak. They are all marked on your map with a golden star. You do not need to use the Tassi Box here anymore.
- Vorrk – Lion’s Arch – need to interact with the corpse. His corpse is located in Western Ward
- Morraloo – Bloodtide Coast – talk to the Quaggan near Sorrowful Sound
- Kasparak – Gendarran Fields – talk to the skritt near Almuten Estates.
June 20
- Two more opens up tomorrow.
Maps if you need
http://dulfy.net/2013/06/19/gw2-every-piece-matters-missing-suspects-achievement-guide/