"We reiterate that this is not an act of terrorism but this incident is confined to the act of one man alone," Manila police chief Oscar Albayalde told reporters after the man was finally identified.
Albayalde said the man was Jessie Carlos, 43, a father-of-three from Manila who had been banned from all casinos in April following a request from his family because of a gambling addiction.
"He is heavily indebted due to being hooked to casino gambling. This became the cause of misunderstanding with his wife and parents," Albayalde said.
The masked man stormed into the Resorts World casino and hotel complex in Manila on Friday with an M4 automatic rifle and a bottle of petrol, before setting alight a number of different rooms in the complex.
Thirty-seven people died in the fires, dozens more were injured in a stampede to escape, and the gunman was found dead about five hours later in a hotel room after committing suicide by setting fire to himself, police said.
'That is not the work of IS': Duterte
IS claimed responsibility, with a report on its self-styled Amaq news agency saying its "fighters" carried out the attack.
Authorities had repeatedly insisted on Friday and Saturday the attack was not terrorism related, rather it was a bizarre robbery attempt by a deranged man.
Albayalde said Sunday the confirmed identification of the assailant proved the initial police theory was correct.
"We will not allow people or any threat group to use this situation to advance their propaganda or personal causes, whether foreign or local," Albayalde said in reference to the IS claims.
Albayalde spoke at a press conference with some of Carlos's relatives sitting next to him.
"They express their deepest sympathy to the families and friends of the victims and to the public in general," he said.
"They share the pain brought about by the act of Jessie. Today, we hope to have brought closure and peace to the bereaved families."
