"He had a gunshot wound to the head and he was really burned", Albayalde said. The suspect was found dead early Friday of an apparent suicide and the gambling chips also were recovered.
The authorities have not yet confirmed who may be behind the attack, but Rita Katz, director of the Site Intelligence Group, which tracks extremist propaganda, wrote on Twitter that a Filipino operative of the Islamic State had said "lone wolf soldiers" were responsible.
Dozens of others were injured in a stampede as they rushed to leave Resorts World Manila, which is across a road from the Philippines' main global airport, after the man fired what police said was an M4 assault rifle and started the fire around midnight.
Around midnight Thursday, the masked and armed gunman forced his way into the second-floor casino and starting shooting at gambling machines and setting tables on fire, according to witnesses and police.
The attack was initially believed by some to be an act of terrorism.
The Philippines have been troubled by terrorism lately, as government forces are battling ISIS-affiliated soldiers for control of the city of Marawi, a mostly Muslim city on the southern island of Mindanao.
Gen. Ronald Dela Rosa says authorities have reviewed CCTV footage from the scene and the lone gunman "was not hurting anyone". He did not hurt the guard but went straight to the gambling area, Dela Rosa said, according to AP.
He stuffed a backpack with gambling chips, fired his assault rifle at TV screens and set tables on fire by pouring petrol on to them from a 2-litre bottle, Mr dela Rosa said.
Johnny Ordanza, an employee of the hotel, said he saw at least one person starting to set tables on fire on the second floor of the casino and firing shots.
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"Islamic State fighters carried out the Manila attack in the Philippines", the news agency said.
Dela Rosa said 18 of 54 injured people were in hospital.
Outside the complex, relatives of people caught inside waited to hear news of their loved ones.
"We are closely monitoring the situation and I will continue to give updates, anything happens, during this period of time", he said.
The suspect took 113 million pesos ($226,000) worth of gambling chips, which were found in a bag he was carrying. US President Donald Trump also branded it a "terrorist attack". "He lay down on the bed, covered himself in a thick blanket and apparently doused himself in gasoline", National Police chief Ronald dela Rosa told reporters in Manila.
Presidential spokesman Ernesto Abella has ruled out a link between the casino attack and the ongoing operation against Islamist militants occupying several neighborhoods of Marawi, who are seeking recognition from Islamic State.
Dela Rosa said there was no immediate indication of terrorism. "I am very anxious as a parent, I need to find her", he said.
The bodies were found in the smoky gambling room by firefighters and all died from suffocation and smoke inhalation, Metropolitan Manila police chief Oscar Albayalde said.
Philippines President Rodrigo Duterte declared martial law over the island of Mindanao in light of the crisis.
The fighting in Marawi broke out May 23 when Philippine troops attempted to capture Isnilon Hapilon, the leader of a terrorist group known as Abu Sayyaf.