Blake lived in Erith, London, with her partner, Arthur Simpson-Kent, and their two sons, Zachary and Amon, who were aged eight and four. Blake was diagnosed with motor neurone disease on 11 December 2015 after first showing neurological symptoms in September 2013.
She had two sons, Zachary (b. 2007 - d. 2015) and Amon (b. 2011 - d. 2015), with her partner Arthur Simpson-Kent.
Blake and her two sons went missing on 13 December 2015. On 16 December, a family member reported her missing to the Metropolitan Police. Police interviewed her partner, Arthur Simpson-Kent, the same day, and he went missing three days later. Her sister said that Blake had wanted to end her relationship with Simpson-Kent "a long time ago".
Blake's car was discovered on 3 January 2016 in Bethnal Green. On 5 January 2016, police searched Blake's home and found three bodies in the garden. They started a murder investigation. On 7 January investigators confirmed that the bodies had been identified as Blake and her two children, and said that they had each died from head and neck injuries.
Police said that Simpson-Kent was being sought in relation to the deaths; the BBC reported that he was believed to have travelled to Ghana in December. On 9 January a Scotland Yard spokesman said that police in Ghana had arrested Simpson-Kent, having travelled there on 19 December; he was remanded for two weeks. Simpson-Kent's lawyer, Justice Srem-Sai, claimed that he should be released from prison until official extradition proceedings were underway. Of the legal process, Srem-Sai said that a "person must be released until you have the legal right to detain them. He was not given his full rights, including access to legal counsel. His right to a fair trial is being denied and is still being denied."
On 26 January, Simpson-Kent appeared at an extradition hearing in Accra, where he told the court that he would voluntarily return to the UK. Simpson-Kent did return to the UK on 12 February 2016 and was arrested at Heathrow Airport, following which, he was charged with the murder of Blake and their two children. On 10 June, Simpson-Kent appeared at the Old Bailey where he formally entered guilty pleas to the murders of Blake and their two sons. On 5 October 2016, Mr Justice Singh sentenced Simpson-Kent to life imprisonment with a whole life order, meaning he will not become eligible for parole and is unlikely to ever be released from prison.
On 6 January 2016, the Metropolitan Police referred itself to the Independent Police Complaints Commission over its handling of the inquiry. Of the referral, the Metropolitan Police said "The Metropolitan Police has today, Wednesday 6 January, made a voluntary referral to the Independent Police Complaints Commission in relation to the Sian Blake missing person investigation. An initial review has highlighted some potential issues regarding the handling and grading of the missing persons investigation. The Directorate of Professional Standards was informed on Monday, 4 January, and is working with the investigation team to fully understand the timeline of police interaction with the family."