Following the court order and exhumation was carried out by Professor Dame Sue Black, an eminent forensic anthropologist.
She concluded that the coffin had been buried without human remains, the BBC reported.
Prof Reid reached her conclusion following the exhumation at Saughton Cemetery in Edinburgh.
The coffin itself had disintegrated. Prof Black, who did discover a hat, shawl, cross and name tag said there were neither skeletal remains nor evidence of decomposition.
"Ultimately there is only one possible logical explanation and that is that the body was not put in that coffin."
Ms Reid, 68, said she was devastated by the findings.
She recalled that when she asked to see her dead son, she was shown the body of a child which was not hers.
"I objected but they said I was suffering from post-natal depression," she said.
"This baby was blonde and big, my baby was tiny and dark-haired. This was not my son."
In the wake of the English inquiry, NHS Scotland admitted the same practice took place north of the border.
Ms Reid is now demanding to know what happened to her son who, she said, deserved a proper burial.
Funeral directors Scotmid Co-operative Funerals said as soon as they heard of the allegations they informed Police Scotland.
A statement said: "We also recently met with Mrs Reid and close members of her family to offer our full support in what has been an extremely distressing situation for them.
"We hope that our actions in contacting the police will help give Mrs Reid the answers to the questions she has raised about her son's funeral."
NHS Lothian deputy chief executive Jim Crombie said: "Our condolences are with the family of Gary Paton. This matter is now being looked into by the police and we are unable to comment further."