Sri Lankan authorities have released surveillance footage showing two of the Muslim suicide bombers riding a hotel elevator at the Shangri-La Hotel in Colombo moments before blowing themselves up at an Easter Sunday breakfast.

The suicide bombers can be seen smiling and talking to each other as they head down to the third floor. Here, they head for the Table One restaurant where they later detonated the explosives inside their backpacks.

Footage from inside the restaurant shows one of their bombs exploding in a bright red flame with smoke engulfing the camera.

A few hours after claiming responsibility for the horrific Easter Day bombings in Sri Lanka that killed 321 people, ISIS on Tuesday released a new video aimed at backing-up its claim.

The unverified ISIS video released through ISIS' Amaq propaganda arm shows eight men standing before the black ISIS flag. All of the men are masked except for one man, who ISIS said was the team leader.

This man was identified in the video as Abu Ubaida. He also led the suicide bombers in a pledge of loyalty to the murderous terror group.

Abu Ubaida was later identified by Sri Lankan officials as Zahran Hashim, a Sri Lankan Muslim preacher and leader of the country's group National Thowheeth Jama'ath (NTJ) terror cell. Zahran is also the suspected architect of the attacks.

"Zahran is the mastermind of these attacks," said Azath Salley, governor of Sri Lanka's Western Province, told the network. "He is the one."

"He is the guy who is giving them the ideology, and when he talks to people, they get convinced."

Hashim had been under watch for at least three years due to his strident calls for violence against non-Muslims, some of that were still posted on YouTube on Monday. YouTube later in the day deleted Zahran's account "for violating YouTube's Terms of Service."

Hashim was a prolific online preacher infamous for his hateful sermons calling for infidels and non-Muslims to be put to death. He once wrote: "Hindus, Christians, Buddhas are Kafirs. Allah created this land for Muslims; only Muslims have the right to rule. Loyalty of Muslims should only be for the Nation ruled by Muslims."

"It was basically a hate campaign against all non-Muslims," said Hilmy Ahamed, Muslim Council of Sri Lanka vice president to the Associated Press. "Basically, he was saying non-Muslims have to be eliminated."

On Monday, Sri Lankan authorities said Hashim and his NTJ were behind the attacks but the group had "international support." Sri Lankan Prime Minister Ranil Wickremesinghe believes Hashim died in the attacks as one of the suicide bombers.

ISIS' al-Amaq news agency claimed responsibility on its channel on the encrypted messaging app Telegram late Tuesday. Its message read:

"The perpetrators of the attack that targeted nationals of the crusader alliance (anti-IS US-led coalition) and Christians in Sri Lanka the day before yesterday were Islamic State fighters."

This article originally appeared in IBTimes US.

Sri Lanka Terror Victims Grave
A priest stands next to graves after a mass funeral near St Sebastian's's Church on April 23, 2019, in Negombo, Sri Lanka. At least 321 people were killed with hundreds more injured after coordinated attacks on Easter Sunday rocked three churches and three luxury hotels in and around Colombo as well as at Batticaloa in Sri Lanka. (Carl Court/Getty Images)