Rainwater had poured into the wood behind the sign, causing it to buckle, and no one had checked to see if the sign and its fixings were still in good condition, Mr Simmons-Jacobs told the jury inquest.
"Unfortunately, it happened on that day with that poor gentleman passing by."
Mr Marx, who was originally from Gisborne, was struck on the head and neck by the sign on January 28, 2013. Several bystanders witnessed what happened, and ran to his aid. They pulled the sign off him before paramedics from a passing ambulance attempted to resuscitate him
He was taken to hospital, but died shortly after.
Off-duty Constable Dylan Wright said he was on his way to the cinema when he heard a "loud snap".
"I heard a scream. I looked over and saw there was a body underneath where the sign had fallen. I immediately ran over," the Islington Gazette reported him as saying. "There was blood coming out from under the sign."
His girlfriend, Natalie Chung, revealed they had planned to get married. They had been together for nine years and had been in London four months.