His alleged killer stood over the Dr Ensink's body as shocked neighbours carried out CPR in a desperate bid to save the lecturer.
"The other guy looked like he tried to stab himself. He pulled his jumper up and pointed the knife at his own body but didn't look like he had the courage to do it."
Mamidato Rodrigues
They said the knifeman even held the knife to his own bare chest before eventually running off. Dr Ensink was pronounced dead at the scene at 1.50pm on Tuesday.
One neighbour, Mamidato Rodrigues, 46, told how she watched from her window as Dr Ensink lay prone between two parked cars near to the pavement.
She said: "It was around 1.30pm, I had been in the kitchen and my daughter was cleaning.
"We heard some screaming from outside, and my daughter yelled at me to come to the window.
"I saw a white man on the floor, lying on his back with his face up and arms out.
"He had blood around the chest area and on his upper body, while another man with a knife was standing near the body.
"A girl ran over and tried to help him, giving him CPR and my daughter called an ambulance.
"The other guy looked like he tried to stab himself. He pulled his jumper up and pointed the knife at his own body but didn't look like he had the courage to do it.
"Then he ran away up the road shortly before the paramedics arrived.
"My daughter told me the guy stabbed the man in the back with a knife about 20cm long and he was left screaming.
"It is a very emotional time for us. It's very hard to see something like this."
Femi Nandap appeared in custody at Highbury Corner Magistrates Court in north London earlier on Friday charged with Dr Ensink's murder.
Mr Nandap, dressed in an all-grey prison-issued with short black hair, spoke only to confirm his name and date of birth.
A post mortem examination was taking place on Friday.
Dr Ensink had been a lecturer in Public Health Engineering at London School of Hygiene and Tropical Medicine since 2008.
He described his 10 years of experience as evaluating the linkages between sanitation, water management and its impact on human health and the environment.
His work took him across the world, including Tunisia, Pakistan, Sri Lanka, Afghanistan, Ethiopia, Ghana, Guinea Bissau, Guinea, Kenya, Senegal, Tanzania, Uganda, and Vietnam.
His specialties included the safe use of sewage in agriculture, and waste water treatment for low income countries.
The London School of Hygiene and Tropical Medicine is a public research university in Camden, north London.
It specialises in public health and tropical medicine and is a constituent college of the University of London.
Founded by Sir Patrick Manson in 1899, it is one of the most prestigious institutions in the world in the fields of public health and infectious diseases, ranking highly in both national and international league tables
Dr Ensink worked at the International Water Management Institute from 1998 to 2006, before moving to London School of Hygiene and Tropical Medicine as a research fellow.
His PhD, Infectious and Tropical Diseases, was undertaken in Pakistan and India on the use of untreated sewage in agriculture and focussed on the association between water quality and the risk of hookworm and other intestinal infections in farmers using untreated wastewater.
Multilingual Dr Ensink, who spoke English, Dutch, French and German, completed his masters degree in Irrigation and Health at Wageningen University in the Netherlands.
Mr Nandap, 22, of Woolwich, south east London, was remanded in custody and is next due to appear at the Old Bailey on January 4.
