Daniel Mohan, whose body was recovered from the water adjacent to Willoughby Place in Enniskillen, was reported missing on April 25, 2010. His body was found five days later on April 30.
A Police Ombudsman's report led to nine police officers, eight of supervisory rank, being disciplined after they failed to locate Daniel in an "expeditious and thorough manner".
At today's inquest, Coroner John Leckey reported that the pathologist had found two illicit drugs BZP and TFMPP in Daniel's system and a low level of the tranquilliser Diazepam. "These drugs are taken for stimulant and euphoric effects," he said.
"I can't help but think that the drug dealer who sold these drugs to Daniel bears some responsibility for this tragedy," he said.
Mr. Leckey said to Mrs. Tracey McMulkin, Daniel's mother, that he was aware that one of her concerns was that Daniel had been attacked or thrown into the river.
"All the evidence was carefully considered by the forensic pathologist . . he is satisfied nothing he found signifies that Daniel was subjected to being beaten up or assaulted. I hope that is reassuring," he told her.
"No, it is not," she replied.
The court heard that there was "no evidence" that Daniel was involved with others in a burglary at Portora School.