The deaths occurred in Todmorden, West Yorkshire, between 1974 and 1975.
He was questioned for 30 hours at Halifax police station in West Yorkshire and later returned to Frankland Prison near Durham.
In January a new investigation was launched into whether the former family doctor had carried out other murders.
The inquiry followed a report that he may have killed more than 200 patients during his 24-year career.
Lethal injections
Shipman, of Hyde, Greater Manchester, was convicted in January 2000 of murdering 15 elderly female patients with lethal injections, and given 15 life sentences.
Since his conviction, he has refused to talk to Greater Manchester Police about further suspicious patient deaths in the area.
In January this year, detectives said that they were to investigate all 22 deaths certified by Shipman when he worked as a GP in Todmorden for 18 months.
West Yorkshire detectives have since liaised with colleagues in Greater Manchester over the inquiry.
Lethal doses
Shipman worked in Todmorden before moving to Hyde in 1977, where he stayed until his arrest.
The GP was convicted of murdering 15 of his female patients by giving them lethal doses of the drug diamorphine - the medical term for heroin.
Most of the women were killed in their own homes, with no-one else present.
The director of clinical governance, research and development at the University of Leicester, Professor Richard Baker, carried out the review of Shipman's clinical practice.
It was discovered that compared with other doctors' rates of patients dying at home, Shipman had an excess of 236 deaths.