Butt, 27, Rachid Redouane, 30, and Youssef Zaghba, 22, killed eight people and injured 48 more in a van and knife attack on June 3 2017.
They mowed down pedestrians on London Bridge before stabbing innocent bystanders at random in nearby Borough Market.
Xavier Thomas, 45, Christine Archibald, 30, Sara Zelenak, 21, Sebastien Belanger, 36, James McMullan, 32, Kirsty Boden, 28, Alexandre Pigeard, 26, and Ignacio Echeverria, 39, all died.
For the deaths of Mr Thomas and Ms Archibald, who were killed by the van, the coroner included a reference to the lack of barriers on London Bridge at the time.
He said: “At the time of the attack there was no form of physical protective security on London Bridge, despite the fact it was a location that was particularly vulnerable to a terrorist attack using a vehicle as a weapon.”
On the investigation into Butt, he said: “I don’t consider the narrative conclusions should criticise MI5 or the police.
The inquest continues.