Story highlights Closed-circuit television footage obtained by CNN provides chilling new details

At one point during the attack, the gunmen took turns to pray

They bowed down in Islamic prayer, taking a break from incessant gunfire

They also chatted on cell phones as they sprayed bullets at shoppers

As they strolled through Westgate Mall, guns strapped to their torsos, the attackers chatted on their cell phones while they sprayed bullets at terrified shoppers.

Ruthless and nonchalant, they randomly gunned down shoppers at the upscale mall in the Kenyan capital.

At one point, they took turns to pray, removing shoes to perform the ritual washing in a room stacked with boxes. They bowed down in Islamic prayer, taking a break from incessant gunfire.

Chilling footage from mall

Photos: Photos: Kenya mall attack Photos: Photos: Kenya mall attack Kenya mall attack – Relatives of Johnny Mutinda Musango, 48, weep after identifying his body at the city morgue in Nairobi, Kenya, on Tuesday, September 24. Musango was one of the victims of the Westgate Mall hostage siege. Kenyan security forces were still combing the mall on the fourth day of the siege by al Qaeda-linked terrorists. Hide Caption 1 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Ann Gakii reacts at the Nairobi City Mortuary after identifying the body of her father, who was killed in the mall attack on Saturday. Hide Caption 2 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A Kenyan soldier runs through a corridor on an upper floor at the Westgate Shopping Mall in Nairobi, Kenya, on September 24, shortly before an explosion was heard. Sounds of heavy gunfire erupted from the mall Tuesday, even as authorities said they had the building under their control. But four days after Al-Shabaab terrorists stormed the swanky mall, several gunmen -- including snipers -- were still inside, two senior officials said. Hide Caption 3 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Kenyan Defense Forces walk near the mall on Monday, September 23. Hide Caption 4 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Kenyan Defense Forces leave the mall on September 23. Hide Caption 5 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Stephen, center, is comforted by relatives as he waits for the post mortem exam of his father, who was killed in Saturday's attack at the mall. Hide Caption 6 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A Kenyan police officer guards the entrance of a building near the mall on September 23. Hide Caption 7 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A Kenyan security officer takes cover as gunfire and explosions are heard from the mall on September 23. Hide Caption 8 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Heavy smoke rises from the Westgate Shopping Mall on September 23. Hide Caption 9 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Medics take cover behind a tree as gunfire and explosions are heard from the Westgate Mall on September 23. Hide Caption 10 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A Kenyan police security officer runs for cover as heavy smoke rises from the mall on September 23. Hide Caption 11 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A paramedic runs for cover outside the mall on September 23. Hide Caption 12 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – People run for cover outside the mall after heavy shooting started on September 23. Hide Caption 13 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Kenyan security forces crouch behind a wall outside the mall on September 23. Hide Caption 14 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Soldiers take cover after gunfire near the mall on September 23. Hide Caption 15 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Kenyan paramilitary police officers patrol the area near the mall on Sunday, September 22. Hide Caption 16 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Soldiers from the Kenya Defense Forces arrive outside the Westgate Mall on September 22. Hide Caption 17 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A woman shields a baby as a soldier stands guard inside the Westgate Mall on Saturday, September 21. Hide Caption 18 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A rescue worker helps a child outside the mall. Hide Caption 19 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – People who had been hiding inside the mall during the gunfire flee the scene. Hide Caption 20 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – An armed official takes a shooting position inside the mall. Hide Caption 21 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – An armed official crouches on September 21. Hide Caption 22 of 51 Photos: Photos: Kenya mall attack Hide Caption 23 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Bodies lie on the ground inside the mall. Hide Caption 24 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Men help a wounded woman outside the mall. Hide Caption 25 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Officials carry an injured man in the mall. Hide Caption 26 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Soldiers move up stairs inside the Westgate Mall. Hide Caption 27 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Armed police leave after entering the mall. At least one suspect has been killed, a government official said. Police have said another suspected gunman has been detained at a Nairobi hospital. Hide Caption 28 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Armed police take cover behind escalators as smoke fills the air. Witnesses say tear gas was thrown in the corridors. Hide Caption 29 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A woman who had been hiding during the attack runs for cover after armed police enter the mall. Hide Caption 30 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A body is seen on the floor inside the smoke-filled four-story mall. Hide Caption 31 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – An injured person is helped on arrival at the Aga Khan Hospital in Nairobi after the attack at the upscale mall. Hide Caption 32 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A soldier directs people up a stairway inside the Westgate on September 21. Hide Caption 33 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – An injured man is wheeled into the Aga Khan Hospital in Nairobi. Hide Caption 34 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – People run from the Westgate Mall. Hide Caption 35 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A Kenyan woman is helped to safety after the masked gunmen stormed the upscale mall and sprayed gunfire on shoppers and staff. Hide Caption 36 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Crowds gather outside the upscale shopping mall. The interior ministry urges Kenyans to keep off the roads near the mall so police can ensure everyone inside has been evacuated to safety. Hide Caption 37 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A policeman carries a baby to safety. Authorities said multiple shooters were at the scene. Hide Caption 38 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Bodies lie outside the shopping mall. Hide Caption 39 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A security officer helps a wounded woman outside. Hide Caption 40 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Elaine Dang of San Diego is helped to safety after the attack. The military asked local media not to televise anything live because the gunmen are watching the screens in the mall. Hide Caption 41 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Paramedics treat an injured man outside the mall. Hide Caption 42 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Medical personnel carry a body away. Hide Caption 43 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A body lies outside the mall. Gunmen shot people outside the mall as they entered it Hide Caption 44 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A woman is pulled by a shopping cart to an ambulance. Hide Caption 45 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A wounded man is escorted outside the mall. Hide Caption 46 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A police officer carries a baby as people keep low and run to safety. Crowds dashed down the streets as soldiers in military fatigues, guns cocked, crawled under cars to get closer to the mall. Hide Caption 47 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – People run away from the scene. Hide Caption 48 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – Armed Kenyan forces take position to secure the area around the shopping mall as ambulances move in to carry the injured. Hide Caption 49 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A woman reacts after she is rescued from the mall. Hide Caption 50 of 51 Photos: Photos: Kenya mall attack Kenya mall attack – A couple flee the area. As night fell, authorities said they had cornered the gunmen in the mall. Hide Caption 51 of 51

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Closed-circuit television footage obtained by CNN provides the chilling new details of what happened during the attack last month.

In part, it shows two people with guns casually walking and shooting their way through a supermarket in the mall. During the hours of video, they are seen talking on the phone, praying and shooting toward anything that moved.

A man whimpering in a pool of blood on the floor crawled to get away. A gunman returned and shot him, again.

In between the gunfire, the attackers scanned ceilings for surveillance cameras. Nearby, shoppers hid behind cash registers while some ran for their lives. Others, too terrified to move, cowered on bloody floors.

Parking lot mayhem

The footage was taken on September 21, day one of the four-day siege. Though the video has no sound, the terror on the faces of the victims is loud and clear.

In addition to the two attackers in the supermarket, the footage shows two more making their way through the parking lot. They opened fire. Shoppers slithered under cars. Others tumbled to the ground, felled by bullets.

The attack left at least 67 people dead , many more injured and dozens unaccounted for.

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Details match up

Details from the footage appear to corroborate a running commentary by the Al-Shabaab, which claimed responsibility for the attacks.

In its Twitter account during the siege, the terror group said the attacks were conducted by men. It denied reports that terror suspect Briton Samantha Lewthwaite was involved.

Al-Shabaab said it remained in contact with the attackers as they battled Kenyan forces during the hostage crisis.

Hostage takers join forces

The attackers in the parking lot later joined the others in the mall. The four wandered, rounding up hostages.

A woman with two children and a third in a shopping cart walked by a line of cash registers. A bloody teenage girl followed them; a gunman pointed the way. The woman, the children and girl were all eventually released.

The footage focuses on the corner of the mall closest to the supermarket, which occupies the anchor position in the four-story mall. The stories repeated themselves in various places at the mall, which has more than 80 stores.

Many unknowns

There are many mysteries about the mall attack.

With dozens still unaccounted for, how many people did the attackers kill? How many terrorists did the Kenyan forces kill? How many civilians and terrorists are buried beneath the concrete chunks of the collapsed section of the mall?

It's unclear whether the four terrorists in the video were arrested or gunned down by security forces at the scene. Even the total number of assailants is unknown.

At the time of the attack, Kenyan officials said that up to 15 gunmen were involved.

On day four, as the operation wound down, President Uhuru Kenyatta said five terrorists were killed and 11 suspects were in custody.

But since then, the numbers have fluctuated, with different officials citing various numbers between four and six.

This month, military spokesman Maj. Emmanuel Chirchir said four gunmen died when part of the mall collapsed. It's unclear whether he was referring to those in the video. Their charred bodies, he said, are undergoing DNA tests.

Chirchir also released the names of the dead militants, including an American of Somali origin, but analysts say those names may be pseudonyms.

Officials have said the answers may be buried beneath the rubble of the collapsed section of the mall.

But, as they scour through the mangled heap, there are more questions than answers.