An Auckland teen who shot four young men - killing one - has pleaded guilty, weeks ahead of his murder trial

Now 20-year old Kayden Stanaway killed 18-year-old Maxwel-Dee Repia outside his Grey Lynn home in September last year, and injured three others.

He faces one count of murder and three counts of wounding with intent.

Court documents revealed in the High Court at Auckland today state the defendant's family had been terrorised in the months leading to the shootings.

The agreed summary of facts deems the quadruple shooting was in self-defence, although so excessive as to be illegal.