At the start, the al-Shabaab gunmen's attack on Nairobi's Westgate mall last month seemed like a distant, horrifying idea.

Even for those of us journalists standing just a short distance away, the gunmen's bloody handiwork inside was largely shielded from view, accessible at the time only through the instant accounts of those unlucky enough to have witnessed it.

Fast forward one month, and through reams of newly released CCTV video, and you see far more than anyone could possibly want.

Suddenly, we are face to face with these ruthless attackers. Young, deliberate men with automatic weapons sauntering into a store while a wave of terrified people recede.

Thankfully, perhaps, there is no audio.

In one scene, we see one unfortunate victim crawl behind what appears to be a display at the front of a store; you can just make out his legs as he lay sprawled on the floor in an attempt to hide.

One of the approaching gunmen spots him, and pauses just long enough to coldly aim and shoot — point blank — before continuing his calm saunter, as if nothing had happened.

Kenya mall CCTV

A gunman with the Somalia extremist group al-Shebaab is viewed on CCTV camera during the attack on Nairobi's Westgate mall in September. (CBC)

It is a chilling, unforgivable moment. The video contains many more.

A little later, when that same man on the floor, now injured and bloody, is trying to get away, another gunmen walks by and, with one more bullet, ends his life.

It is now four weeks since nearly 70 people from an array of countries were murdered in the carnage — a four-day siege organized by the extremist Somali group al-Shabaab.

Now, the video from the closed-circuit TV cameras is raising the earlier insistent questions anew, perhaps even more forcefully.

What goes through the mind of a twenty-something as he pulls the trigger with such eerie nonchalance to end the life of a stranger? What could justify such calculated carnage?

Triumphalism

The al-Shabaab group claimed responsibility for the attack on the Westgate mall, ostensibly in retaliation for Kenya (along other African Union countries) sending its military into Somalia to root them out.

Terrorism experts subsequently described the attack as the grossly underestimated group's graduation to a new level of violent achievement.

Real-time tweets, apparently from a member of al-Shabaab, lauded the attackers (consistently referred to as mujahideen — fighters in a holy war) and cheered them on, insisting there would be no negotiation.

There was something deeply disturbing about such triumphalism when the target was merely a mall full of defenceless shoppers.

But it's this latest video that lays bare the horror, and fuels the outrage anew.

Kenya mall attack police

A police officer tries to secure an area inside the Westgate Shopping Centre where gunmen went on a shooting spree in Nairobi September 21, 2013. (Siegfried Modola / Reuters)

In it we see bullets screaming through a corridor over the heads of shoppers scrambling to stay low. Shopping carts become stretchers to move the wounded. A counter at a cafe becomes a berm protecting a "trench" for the terrified customers to cower in.

In this video we see Westgate the way the attackers did — we see the mall as war zone.

But it's not a war zone. To watch the video is to see well-trained, battle-hardened fighters take on a bunch of Saturday shoppers, many of them in the company of children.

We also watch these young attackers take a moment from preying on the innocent to take turns to pray to God.

To do so, after committing such horrendous crimes, is profoundly unsettling — especially so for those who are certain their religion is incompatible with such acts.

Some of those Muslims, in the U.K., who have spoken out to say exactly that, have now been named as possible al-Shabaab targets.

In a newly discovered online video, prominent British Muslims who criticized these extremists were specifically singled out for retaliation. The police believe the threat is credible and have offered these people protection around the clock.

Little, though, is more disturbing than the CCTV images of the attackers picking off their victims in the incongruous place that they somehow saw as a legitimate battleground for the defence of their ideas and beliefs.

One of the al-Shabaab attackers, now suspected to be a Norwegian national of Somali origin, is seen walking backward, his head swiveling slightly as he surveys his surroundings, before deliberately unleashing a couple of shots at an unseen target.

He moves as if in battle, in the aisle of a grocery store. Some battleground. Some war.