Ya-Haddy Sisi Saye (24), also known as Khadija Saye, Abufars Ibrahim (39), and Anthony Disson (65) all lived in the 24-storey block, which was destroyed by a huge blaze last Wednesday in west London.
Commander Cundy also formally identified the first victim of the fire as 23-year-old Mohammed Alhajali.
When asked why they couldn't get access to it, she said: "Because no one's telling us where it is".
"Sadly, for many families, they have lost more than one family member, and my heart truly goes out to them", he said.
Mr Cundy also promised an "exhaustive" criminal investigation into the fire that would also look at a major refurbishment of the building completed previous year.
Footage from inside the building shows partially melted washing machines and fridges among heaps of twisted metal and other debris.
Composing himself, he said "It's fair to say it is incredibly emotional working in there".
"We must prepare people for the bad reality that some people may not be identified due to the intensity of the fire", he said.
"Sadly at this time there are 58 people who we have been told were in Grenfell tower on the night that are missing, and therefore sadly I have to assume that they are dead".
It ranks above the fire at Bradford City Stadium on May 11, 1985, when 56 people died as flames swept through the wooden stands during a soccer game, according to the Emergency Events Database at the Catholic University of Louvain in Belgium. The investigation will identify any criminal offence that has been committed.
London Mayor Sadiq Khan said Sunday after attending a church service several blocks from the tower that the fatal blaze was entirely preventable.
All the residents of the building will be given £500 in cash followed by a bank payment for the rest from Monday.
"I've investigated major crime for most of my service, and I've seen some awful things".
"Whilst I've said I think there may be changes, I don't think those changes will be as significant as the changes we've seen over the last few days", he said.
"But, frankly, the support on the ground for families who needed help or basic information in the initial hours after this appalling disaster was not good enough".
"Yesterday afternoon following expert advice for the safety of our officers, from the Metropolitan Police the London fire brigade and the London Ambulance arrive, we had to pause that search and recovery".
"As soon as we can, we will locate and recover loved ones", he added.