At least 392 people treated by mental health services either committed or were suspected of committing murder or manslaughter between 2018 and 2023.
Every year on average 65 or more people living with mental illness commit killings, says research by the charity Hundred Families.
The total of victims is almost certain to exceed the number of perpetrators as some kill multiple times.
Attention
The findings come after an independent report revealed NHS failures in treating Valdo Calocane, a schizophrenic who killed three people in Nottingham in 2023.
That tragedy led the headlines but many cases get little attention.
Hundred Families was set up by Julian Hendy to support relatives of people killed by the mentally unwell after his 75-year-old father was killed by a man with a long history of mental illness.
Mr Hendy explained: "I loved my dad, he was funny, he was kind, he was a great man and he didn't deserve to die in the way he did."
After finding a lack of official statistics he did the research himself, sending freedom of information requests to 50 mental health trusts.
Each was asked how many patients had kill...