While searching Laerdan's rooms, you discovered his journal, the passage he had read last marked clearly.
The entry the journal was opened to detailed Laerdan's imprisonment at Sammath Baul and his torture at the hands of Amarthiel and her minions.
You should read further into the journal... it may provide some clues as to Laerdan's purposes.
While reading Laerdan's journal, you discover that Laerdan believes he saw his daughter Narmeleth there at Sammath Baul. This entry is quite disturbing....