Emma Webber said the 14-week public inquiry into the 2023 Nottingham attacks exposed a "catastrophic collapse of responsibility" and an "undoubted miscarriage of justice."
Monday's remarks came after the inquiry concluded Friday, having examined the lead-up to the killings and the aftermath of the June 13, 2023 attacks.
Valdo Calocane, diagnosed with paranoid schizophrenia in 2020, fatally stabbed Barnaby Webber, Grace O'Malley-Kumar and Ian Coates, and tried to kill three others.
Webber said the process had been "brutal, bruising and harrowing" but necessary, accusing authorities of choosing "cover-up over candour" as families press for accountability.