The BBC reported it had been given access to the details by a victim's family member.
The breach of the data concerning the records of Barnaby Webber, Grace O'Malley Kumar and Ian Coates who were stabbed to death by Valdo Calocane was revealed by the Daily Mirror earlier this month.
While some of the staff had legitimate reasons for viewing the records, NUH has confirmed it is investigating a possible data breach.
Dr Manjeet Shehmar, medical director at Nottingham University Hospitals NHS Trust, 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.'