A young widow has tearfully demanded an inquiry into how a psychotic Woolwich man was free to kill the father of her newborn baby days after knife and assault charges against him were dropped.

Dr Jeroen Ensink, 41, was ferociously stabbed to death by Nigerian student Femi Nandap as he left his flat in Islington, north London, in December last year.

The victim had gone out to post cards announcing the birth of his daughter Fleur 10 days before.

When the renowned academic failed to return, his wife, Nadja, went outside to find police had cordoned off the street and the cards her husband had been carrying strewn on the pavement spattered with blood.

Nandap, 23, was suffering from a cannabis-induced psychosis at the time of the killing.

He admitted manslaughter by diminished responsibility and on Monday was handed a hospital order with no time limit.

The prosecution admitted during the hearing that a decision to drop charges of having a knife and assaulting a police officer six days before the fatal stabbing was wrong.

Judge Nicholas Hilliard QC said there was a "dreadful irony" in the case because Dr Ensink dedicated his life to those who he never met and was killed by a stranger.

He described the victim as a "truly remarkable man" adding: "His death is a loss to a large proportion of the world's poor."

The judge added: "I express the hope that those in a position to do so will investigate all aspects of this case and the appropriate lessons will be learned."

Reading her victim impact statement in court Dr Ensink's wife Nadja demanded an independent investigation into failings by both the mental health service and legal system.

The court heard how Nandap came to Britain to study African studies and economic development on a student visa.

In Spring last year, he became psychotic from smoking cannabis and believed voices telling him he was a "Messiah".

In May, he was arrested for wielding a knife in public and punching and biting a police officer. While on conditional bail, Nandap went home to Nigeria where he was treated for mental illness.

His sister informed British police about his condition in August and handed in a certificate saying he was unfit to travel.

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Femi Nandap was suffering a cannabis-induced psychosis when he killed Jeroen Ensink.

On his return in October, Nandap had stopped taking anti psychotic drugs. Then just six days before the killing, charges against him were dropped at magistrates court in December.

Prosecutor Duncan Atkinson QC conceded the decision days before the attack was "not as it should be".

He told the court there had been a review at the "highest level" and the issues involved monitoring on bail and identifying mental illness earlier.

He said the timing of events had raised "a justifiable sense of concern".

Mrs Ensink-Teich brought her baby daughter into court to see the man who killed her husband and "soul mate" sent to Broadmoor hospital indefinitely.

She told the court: "Not only was the love of my life taken from me, but with him also all of our hopes and dreams."

The circumstances surrounding the death of her husband were not a "one off" Mrs Ensink-Teich said.

She said: "This is a terrible tragedy for me and for Jeroen's daughter, and family and friends but it is not a one off; mental health homicides keep happening again and again.

"If such tragedies keep occurring, why has there not been concerted action to address this?

"If a person with a history of mental health problems is found wandering about with a knife, and attacks a police officer, then that person must be referred to a secure unit for proper assessment and treatment and not given bail so easily.

"This represents a failure of the health and judicial system that should protect the public and care for those with severe mental illness."

An inquiry should look into how Nandap was granted bail after being charged with assaulting an officer and wielding knifes in public and why he was free on the day of the killing.

She said an inquiry should examine why the Crown Prosecution Service dropped the earlier charges and deal with whether the person responsible for the decision will be held accountable.

She added: "This may help others from being in the same position my daughter and I now find ourselves in. I hope that our case highlights the necessity to bring about the required changes to existing laws. Lessons will not have been learned until concrete changes in legislation will be implemented."

Dr Ensink, originally from Holland, worked at the London School of Hygiene and Tropical Medicine.

He was a renowned water engineer and a dedicated humanitarian who was committed to improving access to water and sanitation in deprived countries.

Dr Ensink's manager Sandy Cairncross said: "He was killed in his prime and just as he was getting his own research projects under way, with potential benefits to millions of people."