Nottingham triple killer Valdo Calocane’s sentence to an indefinite hospital order will be referred to the Court of Appeal for being “unduly lenient”, the attorney general has said.

Calocane stabbed to death Barnaby Webber, Grace O’Malley-Kumar and Ian Coates in Nottingham on 13 June last year.

The 32-year-old engineering graduate, who has paranoid schizophrenia, pleaded guilty to manslaughter by diminished responsibility, which was accepted by the Crown Prosecution Service last month.

judge Mr Justice Turner handed Calocane the hospital order, adding he would “very probably” be detained in a high-security hospital for the rest of his life.

However, the families of the victims claimed the killer’s sentence had “made a mockery of the system” and called for it to be reviewed.

Speaking outside Nottingham Crown Court after the sentencing, Emma Webber, mother of student Barnaby, said the “pre-meditated” nature of the attacks indicated that they were the actions of “an individual who knew exactly what he was doing”.

Several requests were made to the attorney general, arguing that the sentence was unduly lenient.

And on Tuesday morning, the Attorney General Victoria Prentis KC MP said the sentence would be reviewed.

In a statement, she said: “Valdo Calocane’s crimes were horrific and have shocked a nation. He brutally killed three innocent people and violently attacked three other victims. Their experiences will stay in our minds for a long time to come.

“This was a case that evoked strong feelings amongst so many people. Unsurprisingly, I received so many referrals under the Unduly Lenient Sentence scheme to consider the Hospital Order handed to Calocane.

“My duty as a Law Officer in considering whether sentences may be unduly lenient is to act independently of government, even when it is not easy or popular.

“Having received detailed legal advice and considered the issues raised very carefully, I have concluded that the sentence imposed against Calocane for the offences of manslaughter because of diminished responsibility and attempted murder was unduly lenient and will be referred to the Court of Appeal.

“My thoughts remain with all of Calocane’s victims, as well as their families and friends, who have shown such immeasurable strength during this devastating time.”

In response to the decision to review the sentence, the families of the three victims issued a joint statement welcoming it.

They said: “We were happy to hear that the attorney general has agreed with us that the sentencing given to Valdo Calocane, who so viciously and calculatedly killed our loved ones, was wrong.

“We are optimistic that when this reaches the Royal Courts of Justice for its appeal, there will be an outcome that provides some of the appropriate justice we have been calling for.

“It is important to remember that this is just one part of the tragic failures in this case. The investigation into the mental health trust, the CPS, Nottingham, and Leicestershire Police continue.

“We maintain that serious failures in all three agencies must be fully addressed. Organisational and individual accountability must be taken, and where relevant, proper change must be made.”

During the sentencing hearing in January, Miss O’Malley-Kumar’s father, Dr Sanjoy Kumar, told Calocane he was a “cold, cowardly and calculating killer”, while the family of Mr Coates described him as “a selfish monster who decided to go on a spree killing”.

Chilling CCTV showed Calocane returning from London on 12 June, before spending hours prowling the streets of Nottingham before he launched his deadly attack at around 4 am on Ilkeston Road.

He pulled a “double-edged fighting knife” from his bag and repeatedly stabbed history student Mr Webber while aspiring medic Miss O’Malley-Kumar tried to defend him until Calocane turned his attention towards her.

Afterwards, he travelled to Magdala Road and lured Mr Coates towards him before knifing him in the chest and stealing his van, which he used to drive into the town centre and mow down three pedestrians.

He was tasered upon his arrest and went on to plead guilty to the three additional counts of attempted murder.

The court heard that Calocane had a history of mental health issues and had been hospitalised on four occasions, yet had a history of evading welfare officers and refusing to take his medication.

For years, he had experienced psychotic delusions in which he believed he was being targeted by “malign forces” and agencies such as MI5 and had numerous outbursts in which he had assaulted a police officer and two colleagues.

Dr Sanjoy Kumar previously said the failure to charge him for several previous violent incidents formally was a “missed opportunity” that may have “altered his course”.