Police are trying to trace anyone who may have seen a teenager who died after taking illegal drugs in the hour before he became unwell.
Josh Reeson, 15, was found in the Fulford area of York on 27 September and died later in hospital.
Officers said they have established his whereabouts before he was taken ill.
Six people, aged between 14 and 37, arrested in connection with his death have been released pending further investigation.
North Yorkshire Police said Josh and a friend, 14, left an address on Fulford Road at about 03:10 BST and walked towards the city centre, before doubling back onto Broadway West.
The teenagers then walked back to Fulford Road and met another friend, a 14-year-old girl, near the junction of Maple Grove,
It was then that Josh became unwell and a relative of his friend called an ambulance and stayed with him until it arrived.
Officers wish to speak to anyone who may have seen the teenagers between 03:00 and 04:00 and have also asked anyone driving in the area who may have dashcam footage to contact them.