The Ghostly Apparition

The Ghostly Apparition is a side quest available in Saradush Prison.
 * On the east side of the prison, you will be met by a ghostly apparition that will hold its head in agony. Take the skull from the chest nearby.
 * Later on, you will meet the apparition again and it will point to its neck. In a nearby cell, you will find a rusted amulet.
 * Put the skull and the rusted amulet in the cell next door and the apparition will appear again, asking you to sanctify his grave.
 * If you have any Elven Holy Water on you, you will use it to sanctify his grave and the apparition will take you to a cell in which you will find the Bronze Ioun Stone.

Sources & references

 * Baldur's Gate II section at Mike's RPG Center