Freeing him will give the Dragonborn knowledge of the location of his treasure, via Velehk Sain's Treasure Map, while banishing him will yield a Scimitar. The Dragonborn can then choose to banish the Daedra or free him.
When the rings are in place, Velehk Sain is summoned by the glove. Little finger - Pithi's Ornamental Ring.Middle finger - Treoy's Ornamental Ring.Index finger - Katarina's Ornamental Ring.Upon retrieving the rings from the chest, the Dragonborn can return the rings to the relic to summon the Daedra trapped within. The bits of evidence recovered from the scene can be found in the Investigator's Chest (master lock) inside the Arcanaeum.
The Dragonborn discovers some notes lying nearby on a table, the Midden Incident Report, detailing the investigation of the failed summoning.
