The 34-year-old was arrested after he found the body of his mum, Deborah Neale, 60, at Cudworth post office, where she lived and worked.
Ms Neale was found dead on Friday, April 19, 2019 and because her death was initially unexplained, a murder probe was launched.
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Her son and her 57-year-old ex-partner were arrested because they were both at the scene when emergency services arrived.
But yesterday – just over a year later – an inquest into Ms Neale’s death was held in Sheffield and an ‘open conclusion’ was recorded.
It could not be ascertained for certain why Ms Neale died, but she had a history asthma, the lung condition COPD, epilepsy and substance misuse, the inquest heard.
Assistant coroner Tanyka Rawden said: “I think it was a seizure but what we don’t know is how that seizure was brought on. I imagine it was a combination of everything.”
There was no evidence of foul play.
DC Louise Little, of South Yorkshire Police, told the inquest that after police interviews, door-to-door enquiries and an examination of CCTV footage there was ‘no evidence to indicate any third party involvement’ in the death.
In a statement released today, South Yorkshire Police said: "The murder investigation ruled out any third party involvement in Deborah’s death and therefore the criminal investigation has ceased.
“The suspects we’d arrested were released without charge.”