Murder knife

The Murder Knife is an optional dialogue device used to dispose of characters unexpectedly in Dragon Age: Origins, and it is to return in Dragon Age II.

Ruined Temple

 * Brother Genitivi - If the Warden refuses to let Brother Genitivi tell others of the Urn of Sacred Ashes, he walks away from the warden shaking his head. The warden pulls the knife out and throws it at Genitivi. Brother Genitivi turns around to show the knife stuck in the back of his head. He then falls to the ground, dead.

Ostagar

 * The prisoner at Ostagar - He offers you a key in exchange for some food. You choose to kill him and take it. As you draw the knife and start walking towards him he screams for help but you stab him in the heart and kill him.
 * Dog - In the camp at Ostagar you will find a Man caring for a sick mabari hound. He asks you to go in and put a muzzle on it so that he can medicate it. You have the option when you enter to draw the dagger and kill the mabari. This is one of the ocasions where the screen turns black and you do not witness the killing.
 * Pick - If you fail at persuading him into giving you Ser Garlen's Sword, then you will be given the choice to stab him in the stomach.

City Elf Origin

 * Man in dining hall - While sneaking into the castle you will be confronted by a group of Humans sitting in the dining hall. If you have weapons on your back they ask you where you got them. Unable to think of an excuse you exclaim "Oh sod it" and throw the knife across the room. It hits one of the men in the neck, killing him.

Korcari Wilds

 * Wounded Soldier - While preparing for the joining in the Korcari Wilds you find a wounded soldier who's regiment was wiped out by Darkspawn. You have the option of saying you do not have time to help him and slit his throat.

Lothering

 * Greedy merchant - In Lothering there is a greedy merchant who is argueing with a woman from the chantery about him overpricing food. You can drive the sister away and then slit the merchants throat.

Castle Redcliffe Dungeon

 * Jowan - In Redcliff you find Jowan locked in a cell. You have the option to stab him through the cell bars.

Castle Redcliffe

 * Connor - If you helped the Templars destroy the Circle and killed Jowan. You will have the option of killing Connor with the Knife or allowing Arlessa Isolde to do the deed instead.

Redcliffe Village

 * Lloyd - After asking the barkeep to help defend the village with a low cunning/persuade, this will give you the option of throwing a knife into his back.

Random Encounters

 * Zevran - After he ambushes you on the Long Road, you can wake him up to question or slit his throat.
 * Bandit Leader - As part of Leliana's quest, you can let him leave or slit his throat.

East Brecilian Forest

 * Danyla - In the East Brecilian Forest, a dalish elf turned werewolf asks you to end her pain and kill her. If the warden agrees he/she will stab her in the chest, to which she thanks you for.

West Brecilian Forest

 * Deygan - In the West Brecilian forest, a wounded dalish elf you encounter. You can choose to kill him while he is still unconscious.

Dust Town

 * Nadezda - You have the option to kill her during the Entering Jarvia's Hideout quest, acting as if she betrayed the Warden to Jarvia.

Circle of Magi

 * Godwin - During the "Precious Metals" quest with the right dialogue choices, you get the option to slit his throat. ("This is only available if you have been to Orzammar and talked to Rogek, before doing the Broken Circle quest")

Arl of Denerim's Dungeon

 * Vaughan - During the "Rescue the Queen" quest, Vaughan is locked in the dungeon by Rendon Howe. You can use the option "No ones missed you".
 * Rexel - During the "Rescue the Queen" quest, Rexel is locked in the dungeon by Rendon Howe. You can choose to put him out of his misery.

Uses in Dragon Age II
The Murder Knife is to return, albeit much more improved this time. You will once again be given the option of killing your enemies, or people who get in your way.