No police officers face misconduct action over a man who set fire to his mother-in-law and then himself.
Kieren Lynch, 50, set alight to 72-year-old Jennifer Cronin in her garden in Benfleet, Essex, on 13 March 2018 before killing himself.
An inquest in January found arrests not being carried out and poor communication contributed to the deaths.
But an investigation ruled there was no misconduct case to answer.
The Independent Office for Police Conduct (IOPC) report did conclude, however, that seven officers received management action in relation to record keeping and processing information while Essex Police said another officer had received management action in relation to suspect management.
Mrs Cronin, whose daughter Susan Lynch had been divorcing Mr Lynch after 25 years of marriage, died just over two weeks after the attack in Boyce Green.
Mr Lynch had been arrested on suspicion of causing criminal damage on 11 January 2018 and was given bail conditions not to contact his family or attend the family home.
But despite Mrs Lynch reporting multiple incidents between 7 March and 12 March, he was not arrested.
The IOPC report said: "The evidence obtained during the investigation indicated that, while there was a lack of clarity regarding breaches of domestic abuse offences, in particular regarding the responsibility for arrest between the local policing teams and specialist domestic abuse team, there was also a lack of positive action from officers in both teams."
Mrs Lynch had previously said she felt "extremely let down" by Essex Police.
Essex Police has said it accepts the findings of the report.
Det Ch Supt Steve Worron offered his condolences to the family of Mrs Cronin and said the force could have done more to keep her safe.
He said: "Essex Police is a force that promotes learning and improvement and as such we are continually reviewing our working practices and making changes where they are needed."