After a search using a police helicopter, his body was found face-down in a puddle under a railway bridge near the village of Stainton, three miles from his home. He had gone for a walk with a 13-year-old girl who has learning difficulties and another three-year-old boy.
Recording the open verdict, the Doncaster coroner, Stanley Hooper, said it was unlikely Louis had died accidentally, but the burden of proof was not sufficient to prove that it was deliberate.
He said the 13-year-old girl and the three-year-old boy could not be prosecuted because of their age and limited understanding of the incident.
"It seems likely Louis died unlawfully but I am not satisfied this can be proved," Mr Hooper said. "Much of the evidence is second-hand and comes from unreliable witnesses. The Crown Prosecution Service has decided there's going to be no prosecution arising from this tragedy and I respectfully agree with that."