Detectives investigating the death of a woman whose husband went on to murder his fiancee have arrested a 57-year-old man.

Diane Stewart’s death in 2010 at the age of 47 was not originally treated as suspicious and an inquest ruled she had died of natural causes. But police reopened the case shortly after her widower, Ian Stewart, was convicted of the murder of the popular children’s author Helen Bailey last year.

Police would confirm only that they had arrested a man aged 57 from Bedford. The arrested man was released under investigation, police added.

Stewart was sentenced to life in prison, with at least 34 years to serve, at St Albans crown court in February 2017 after being convicted of Bailey’s murder.

Ian Stewart told the court he met Bailey, the millionaire author of the Electra Brown series, on a Facebook group for widowers and widows after the death of his wife, Diane, in 2010. Bailey’s husband, John Sinfield, had drowned during a holiday to Barbados in 2011.

On Wednesday, Hertfordshire police said: “Detectives from the Bedfordshire, Cambridgeshire and Hertfordshire major crime unit have arrested a man following a re-examination of 47-year-old Diane Stewart’s death at her home in Bassingbourn on June 25, 2010.

“The 57-year-old man from Bedford was arrested on Tuesday, 21 August and questioned on suspicion of murder before being released under investigation.”