Detective Constable Damon Deans-Cane believed Clare Cruttenden had faked being burgled after she was found at her home in Quebec Road, St Leonards with her hands and feet bound and tape over her mouth.
The 30-year-old had a history of making allegations to the police, some of which were believed to be false, and Mr Deans-Cane admitted he “saw red” when attending her home in February 2014.
She was found in a coma two days later at the Granville Hotel, in Brighton, after taking an overdose, and later died in hospital.
The mother-of-three had left a suicide note and a jury concluded she took her own life at an inquest.
Mr Deans-Cane was sacked without notice by a misconduct panel in 2015, after it concluded he took a “bullish, assertive and confrontational stance” with Ms Cruttenden, which was “grossly inappropriate”.
It also found she was “vulnerable” and that he had failed to follow “basic steps of investigation and victim care”.
But he was reinstated by a police appeals tribunal in October last year, after fresh evidence was put forward – including positive testimonials about the detective’s career.
However, his case will now have to be heard again after the Chief Constable of Sussex Police, Olivia Pinkney, successfully challenged the tribunal’s decision at the High Court.
Mr Justice Supperstone, sitting in London, said the original panel was “entitled” to dismiss the detective and the appeal decision should be overturned.
He added: “In my view, the panel was entitled to conclude that it did not have confidence in retaining him as an officer...
“I am left in no doubt that the tribunal erred in finding that the sanction imposed by the panel was unreasonable.”
The judge said the case should now go back to the misconduct panel for a fresh decision.
• If you have been affected by any of the issues raised in this article, the Samaritans may be able to help – the charity’s helpline number is 116 123.