New York skyscraper mass shooter assembled weapon himself, police say

Authorities are piecing together days preceding Monday's attack in which four people died in Manhattan office tower

The man who stormed a New York City skyscraper and shot dead four people before he took his own life early on Monday had constructed the rifle he used himself, from parts, the police have said.

The authorities are questioning an associate of the suspect about supplying components of the AR-15-style assault rifle used in the attack.