The police watchdog is investigating the contact that a force had with a mother and her former partner who were killed in a house explosion.
Joanne Shaw, 35, suffered fatal injuries in the blast at her home in Sterncourt Road, Bristol, on 3 May.
Her ex-partner, Ryan Kelly, 41, also died in the incident following the activation of an explosive device.
Ms Shaw had been in touch with Avon and Somerset Police four days before her death, the Independent Office for Police Conduct (IOPC) said on Tuesday.
Its probe would now look at what steps were taken by the force to safeguard her for the five years before the incident, the IOPC said.
Police previously said a call was received from a person inside the house at 6.17am on 3 May reporting a domestic-related incident, saying a man they knew had forced entry to the house.
The caller remained on the line while officers were sent to the house and at 6.30am the caller told police the man was believed to be in possession of an explosive device.
About two minutes later there was an explosion at the property, in which Ms Shaw and Mr Kelly died.
IOPC director Derrick Campbell said there was "a significant history of police involvement in relation to Mr Kelly's behaviour, including allegations of stalking, harassment and assault which we need to examine as part of our investigation".
Emphasising that the organisation was independent of the police, he said investigators were looking into "extensive documentation detailing that history as part of our inquiries".
Ms Shaw's death is being investigated as a homicide by the force, which believed the explosion was deliberate and was not looking for anyone else in connection with her death.
Three other people, including a child, suffered minor injuries.
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Separate opening inquests heard Ms Shaw died from a "penetrating fragmentation blast injury to the chest and pelvis", while Mr Kelly suffered "blast injuries to head, neck, torso and limbs".
Inquests are due to resume in August at Avon Coroner's Court.
Following the explosion, officers along with fire and ambulance crew arrived soon afterwards.
Residents in neighbouring properties were evacuated as a precaution and searches were carried out by the Army to ensure the area was safe.
Searches also took place at an address in Speedwell where Mr Kelly lived. No evacuations were required at that location.
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