Police who investigated a former GP cleared of murdering three patients are to hand files into the deaths of 12 more patients to the coroner.
Dr Martin was supported throughout by his wife Theresa
A jury at Teesside Crown Court cleared Dr Howard Martin, 71, of the charges following a six-week trial.
He denied killing Harry Gittins, 74, Stanley Weldon, 74, and Frank Moss, 59, all from County Durham.
The former GP used to practise in Newton Aycliffe, but now lives in Penmaenmawr, North Wales.
Dr Martin was cleared of murdering the three men with morphine overdoses.
The 12 cases being referred to the coroner have already been considered by the Crown Prosecution Service but no charges were brought due to insufficient evidence, police confirmed.
It has emerged that Dr Martin worked in the same health centre as mass murderer Dr Harold Shipman for 18 months during the 1970s.
But police stressed this was never a line of inquiry in their investigation.
Det Supt Harry Stephenson said: "The Howard Martin inquiry was a different investigation to that of Harold Shipman. We never linked the two inquiries."
Durham Police said they intended to hand a further 12 files to the city's coroner Andrew Tweddle, as a result of other complaints not covered at Dr Martin's trial.
Det Supt Stephenson said: "Ultimately it will be for him to decide what action to take and what parameters he intends to set for any public hearing."
He added the police inquiry had initially concentrated on the period between January 2002 and May 2004 but also embraced relatives' concerns dating back to 1978.
"What we have is we've had 28 people who have made complaints about the practises of Dr Howard Martin," he said
"Three have resulted in a court hearing in which he was acquitted and we totally accept that acquittal.
"But there are 25 lots of people who have made complaints and we're duty bound both legally and morally to investigate those and pass the facts to the coroner."
Dr Martin's lawyer Sara Mason said: "Dr Martin is not in a position to comment in relation to any individual patients."
She added that the CPS had previously found insufficent evidence to bring charges against Dr Martin in relation to the deaths of any other former patients.