A CCTV image of a woman police are trying to trace after a man collapsed and died in Grimsby has been released.
Patrick Donoghue, 35, died after collapsing in an alleyway near McDonalds restaurant in Victoria Street at about 13:00 GMT on 6 September.
Three men and a woman held on suspicion of being concerned in the supply of a class A drug have been bailed.
Humberside Police said it believed the woman was not connected to the incident but could help its investigation.
Det Insp Alan Curtis said: "The woman police would like to speak to and who is shown in the CCTV still, is thought to have walked along the alleyway as a passing member of the public around the time of the incident.
"She is not believed to be connected in any way but it is possible she may have some information which may assist our enquiries."
A post-mortem examination on Mr Donoghue proved inconclusive and police said it could not confirm at present whether his death was suspicious.
Officers are still trying to establish where he is from.