The SIU was called to investigate after Irn Mace, 17, and Alex McCormack, 17, were found near the bottom of the Claremont Access about 6:20 a.m. June 16.
The SIU probe was triggered by an encounter between a Hamilton officer and the teens shortly before they died.
Less than an hour before they were found dead, an off-duty officer on his way home noticed them standing atop an overpass and was concerned enough to check on them three times.
On his third pass he stopped and warned the pair that what they were doing could be dangerous.
"On the basis of this investigation, there is simply no credible information that the subject officer was in any way responsible for the deaths of Mr. McCormack and Mr. Mace," said SIU director Ian Scott.
"On the contrary, in his off-duty capacity, he was attempting to avert what he very reasonably perceived to be a potential accident or misadventure."
According to the SIU statement released Friday afternoon, "the young men appeared to have a prearranged plan to commit suicide, a plan they tragically fulfilled shortly after the subject officer left the area."
The SIU assigned four investigators and two forensic investigators to the investigation. Investigators conducted 12 interviews, examined communications recordings and obtained suicide notes left by the young men.
The SIU investigation determined that early June 16, the Saltfleet District High School students went to the Arkledun Avenue overpass overlooking the Jolley Cut.
"At 5:30 a.m., the subject officer reported off-duty and headed home. He drove up the Claremont Access and saw the two youths standing on the overpass. One was sitting atop the railing and the other was standing against it with his forearms draped over the top.
The subject officer reported his findings to a HPS dispatcher, drove to the top of the mountain, and then returned to the overpass due to concern for the youths' safety. They were now standing in a safer position and he continued on.
He then turned around to go back up the mountain to return home. This time, he noticed the young men were both straddling the railing with their hands behind their backs. He stopped his vehicle, and both young men quickly climbed down from the railing and apologized to him.
The subject officer had a brief conversation with them, stressing that what they were doing was unsafe. The boys apologized again, and then walked away as the officer watched. He left the scene," the SIU statement said.
By 6:30 a.m., the SIU said, a passerby walking over the Arkledun Avenue overpass saw the bodies of the two 17-year-olds lying in the gorge.
A post-mortem at Hamilton General Hospital determined that the cause of death for both teens was blunt force trauma from their fall.