In the Shrine quest for Mephala.

You have to kill the leaders of two families and put clues to start a war between them...

I killed both Horl Ulfgar and Nivan Dalvila... but what do I have to use to incriminate the other family ?

Tried weapons, keys, clothes from the other family... nothing does the job...

Place Davillu Ceremonial dagger in Ulfgar's body,and put the Ulfgar's familiy ring in the Dunmer's body.

Both the above mentioned items can be found in their houses in pretty open locations.