Mental health problems may more often be a factor in homicides than gang membership, with most killings potentially preventable, a study suggests.
The research for London’s violence reduction unit, published on Monday, is the deepest look at homicides in the UK so far, project leaders believe.
Fifty killings were selected from confidential murder case files held by the Metropolitan police. Behavioural insight experts looked for patterns about those killed, their attackers and, most crucially, why. It is hoped that researchers will be able to work out how many could have been prevented and by what means.
Ed Bradon, the director of the project, said the work so far suggested most homicides may be preventable: “Every single one of these 50 homicides could have been prevented at some point. It may not be immediately visible.”
In one case of a domestic homicide, neighbours heard shouts from the home where a woman was killed, but were used to hearing them and so did not call the police.
Bradon said: “A lot of unusual stuff has to happen for someone to be murdered.”
Six factors were identified by studying the 50 cases in depth. Police had already identified key factors behind them but the behavioural insight experts reassessed them.
The key factors for either the victim or killers were mental ill health, a factor in 29 cases; drugs, which were a factor in 26 killings; alcohol, a factor in 16 cases; gangs, a factor in 14 cases; and social media, a factor in 14.
Also identified as a factor was the length of time it took for events to escalate into a killing after a trigger event. In domestic homicides that could be someone deciding to end a relationship, or in a gang killing the robbery of a rival’s drugs. One or more of these factors were identified in the 50 cases examined.
Bradon said: “Mental health appears to be more of a factor than previously realised.”
Some killers had withdrawn from treatment, while others had mental health problems and had never been treated. Mental health, as well as the other key factors, can make the victim more vulnerable to violence, the study says.
Most victims – 28 of those studied – knew their killer, compared with those fatally attacked by a stranger, which happened in seven cases.
Lucy Makinson, who managed the project, said different factors posed a greater risk for different age groups, such as gang involvement for younger people and mental health for older people.
The report calls for young people to be offered help if they face social media threats or taunts, which can be part of the lead-up to a homicide. Makinson said: “Social media is being used to build up tension and is much more common with gang cases.”
Det Supt David Kennett from the Met police said: “This new framework shows tremendous promise, and means for the first time we can truly influence the criminal justice system by identifying where the risks lie.
“There are many contributing factors to each homicide. This new framework will help us work towards preventing homicides from both a policing and partner perspective.”
Some if not most of the extra prevention work would not fall to the police but to other agencies.
The mayor of London, Sadiq Khan, who funded the study as part of violence reduction work, said: “Part of our approach is better understanding why homicides happen, and that’s why my VRU funded and commissioned this groundbreaking framework. If we are to continue reducing violence in London, it’s crucial that we identify more opportunities to intervene early, because I firmly believe that violence is preventable, not inevitable.”
London averages about 130 to 150 homicides a year, and the Met commissioner, Sir Mark Rowley, has said he hopes to cut that number to below 100. The study found each killing costs the police and criminal justice system more than £800,000, and in total over £100m a year in London alone.
The next stage of the research will examine 300 cases of homicide.
• This article was amended on 15 November 2022. Ed Bradon said that “a lot of unusual stuff” has to happen for someone to be murdered, not “a lot of usual stuff” as an earlier version said.
