They have also received two video recordings of the incident.
The officer in charge of the inquiry, Detective Senior Sergeant Rhys Johnston, said police were extremely fortunate that two members of the victim's family had the good sense to video record the incident on their cell phones.
"The events are all captured clearly. It's fair to say that these recordings provide excellent evidence and have assisted us greatly in this inquiry."
The victim remains in a critical condition following surgery on Saturday and Sunday.
Police will conduct further inquiries in the area today and encourage any witnesses to contact the Kaikohe Police on (09) 405 2960.