Peter Foster, who was jailed for life for murdering his police officer girlfriend, has been found dead in his jail cell.
Foster, 36, killed Heather Cooper at their home in Haslemere, Surrey, in a savage attack in which he beat her over the head with a baseball bat and then stabbed her in the throat.
The murder, on October 16, 2011, was witnessed by the couple's three-year-old son, Joshua. They also had a three-month old girl, Isabel.
He admitted the murder at Lewes Crown Court and was sentenced to 17 years. Guards found him hanged in his cell in the early hours of 30 July.
A spokesman for HM Prison Service said: "Prison staff tried to resuscitate him and paramedics were called but he was pronounced dead.
"As with all deaths in custody, the Prisons and Probation Ombudsman will conduct an investigation."
During Foster's trial, Philippa McAtasney QC, defending, revealed that he had tried to kill himself while on remand and had been sent to a mental health wing of the prison.
In sentencing, Judge Richard Brown described him as an "extremely dangerous individual" who had carried out a "wicked, savage and senseless attack".
Cooper's parents, James and Caroline, provided an impact statement to the court. They said: "Heather would have been devastated to know she would not be able to bring up her children and Isabel would never know her mummy and Joshua would suffer grief at such a young age."
Cooper had been an officer with Surrey Police since 2003. Foster resigned from the force in 2009.
It was the second suicide at Lewes Prison in four days. Nathan Vaughan-Jones, 34, faced an 11-year sentence for the manslaughter of his stepfather Nigel Ross and hanged himself in his cell on 27 July.