The 23-year-old barefoot killer, smiled as he repeatedly knifed his victim, who had been on his way to post cards to relatives telling them the good news about the birth.
Mrs Ensink-Teich, who took the couple’s baby daughter, Fleur, to court to see Nandap sentenced for the killing, demanded that more was done to protect the public from those suffering from severe mental illness.
Six days later he attacked and killed Dr Ensink, telling police who tried to intervene that he was the “black messiah”.
Speaking outside the Old Bailey, where Nandap was given an indefinite hospital order, Mrs Ensink-Teich, said there were no winners in a case such as this, but hopefully measures would now be taken to prevent a similar tragedy happening again in the future.
She said: “This represents a failure of the health and legal system that should protect the public and care for those with severe mental illness.
“I hope that following Jeroen's death, an independent investigation will take place and answers will be provided to these simple but pressing questions.
“Why was this individual granted bail after assaulting a police officer and wielding knives in public?
“How can this individual, who was mentally unwell and armed with knives have been at liberty on the day he killed my husband?
“Why on the 23 Dec 2015 did the crown prosecution service drop the knife possession and assault charges against this individual just six days before he killed Jeroen?
“Will those who made that decision in some way be held accountable?
"This may help others from being in the same position my daughter and I now find ourselves in.”
She added: “The lesson will not have been learned until concrete changes have been implemented”
Not only was the love of my life taken from me, but with him also all of our hopes and dreamsNadja Ensink-Teich
The Old Bailey heard how Nandap developed mental health problems after he began smoking a large quantity of cannabis while studying in Boston in the United States in 2012.
Two years later he moved to London after gaining a place at the School of Oriental and African Studies (SOAS).
But last May he was arrested in Edmonton, north London after punching and biting a police officer. When he was arrested he was found with two kitchen knives.
He was charged in connection with the alleged offences but was granted permission to return to his native Nigeria in June on condition he returned to the UK in August to attend court.
When he failed to appear his sister, who also lives in London, provided police with a letter detailing treatment he had been having for his mental health conditions.
After returning to the UK he appeared in court but despite having breached his original bail conditions, was not remanded into custody.
He was was never prosecuted for the bail offence, and the CPS dropped the knife and assault charges on 23 December due to 'insufficient evidence'.
The prosecution admitted that the decision to drop the charges six days before the fatal stabbing had been wrong.
Judge Nicholas Hilliard QC said Dr Ensink, who had devoted his career to helping improve water sanitation for the world’s poor, was a truly “remarkable man”.
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.”
Julian Hendy, of campaigning charity Hundred Families, echoed the call for an inquiry and said: “We are deeply concerned that seriously unwell people are not getting the diagnosis and treatment they need, which is leading to more and more tragedies like this.”