An NHS trust is investigating claims its staff illegally accessed the medical records of the Nottingham attack victims.
Nottingham University Hospitals Trust is looking into claims medics may have hacked into A&E notes made hours after Barnaby Webber, Grace O'Malley-Kumar and Ian Coates were killed by paranoid schizophrenic Valdo Calocane on June 13, 2023.
Their families have been informed of the news and described it as "distressing and traumatic".
They added: "These are not just alleged data breaches but gross invasions of privacy and civil liberty.
"For individuals to choose to access information regarding the vicious attack and murder of Barney, Grace and Ian with no reason to do so is sickening. It's gross and inexcusable voyeurism at the most repugnant level."
They first learned of the potential breach, which was first reported by the Daily Mirror, in a letter from Dr Manjeet Shehmar, the trust's medical director.
The letter says a senior staff member reported a doctor for allegedly accessing the records for no legitimate reason. An investigation was launched and police have also been informed.
It comes after the Care Quality Commission (CQC) identified five missed opportunities to deal with Calocane's violent psychosis in the three years before the killings, in a report published last year.
He was sectioned under the Mental Health Act four times before NHS services lost track of him and then discharged him, the report found.
Earlier last year, it emerged that officers with Nottinghamshire Police described the victims as having been "proper butchered" in WhatsApp messages.
Dr Shehmar said: "We are currently investigating concerns that members of staff may have inappropriately accessed the medical records of Ian Coates, Grace O'Malley-Kumar and Barnaby Webber.
"We have informed the families and will continue to keep them updated throughout the investigation. The families of Ian, Grace and Barnaby have already had to endure much pain and heartache and I'm truly sorry that this will add further to their suffering.
"Through our investigation, we will find out what happened and will not hesitate to take action as necessary."
Calocane was sentenced to an indefinite hospital order in Jan 2024 after admitting manslaughter by diminished responsibility and attempted murder.
Last month, Sir Keir Starmer told the families that a public inquiry led by a judge will take place in "a matter of weeks".
Solicitor Neil Hudgell, who represents the families, told the Daily Mirror: "Every week seems to bring fresh trauma to an already appalling situation. We are actively seeking a complete audit trail of who accessed records, when and for what purpose.
"We want to know whether any unlawfully accessed material has been shared."