Samantha Lewthwaite, the Northern Ireland-born woman dubbed the 'White Widow', slipped out of the Kenyan shopping mall after smearing blood over her face, security sources in the country have said.
They also revealed how Lewthwaite, who was born in Co Down, rented a unit at the Westgate Shopping mall months ago in preparation for last week's terror killing spree.
She hung up newspapers around the shop unit to conceal what was going on inside, pretending to be stocking up on goods.
Staff have told police in Nairobi they helped a woman fitting the description of Samantha Lewthwaite lift boxes into the shop unit.
Witness accounts reveal a woman closely resembling the 29-year-old mother of three was seen being led away among panicked survivors, her face and upper clothes splashed with blood.
Interpol has issued a "red flag" international arrest warrant for Lewthwaite, based on intelligence that she led the attack and escaped.
Shocking stories about the brutalities inflicted by the terror gang are beginning to emerge. Children were among those deliberately killed and there are reports that an infant was decapitated and the head thrown at Kenyan soldiers during the four-day siege.
It is now believed Lewthwaite was the leader of the 13 to 17 terrorists who carried out the attack, but slipped away while the others were cornered by Kenyan soldiers.
The reports strongly contradict some of the impressions given last week that Lewthwaite was merely a book-keeper or finance raiser for the al-Qaeda-affiliated Somali group, Al Shabaab.
Kenyan police have been searching for Lewthwaite since it emerged she took up residence there in 2011 after spending three years living under false identities in South Africa. They believe she had already established links with the Somali terror group Al Shabaab and married one of its senior figures. Her second husband was shot dead in a police raid in Mombasa last October, according to sources.
The Kenyan police believe Lewthwaite, who was born in Banbridge, but was brought up in Buckinghamshire where she converted to Islam in her teens, was the prime mover behind the Westgate Shopping Mall attack, a key target for the Islamist terrorists because it is Israeli-owned.
The police named Lewthwaite as an Al-Shabaab member last June after arresting another British-born member of the group, Germaine Grant. They believe Grant was the terror group's financier working under Lewthwaite. The police believe Lewthwaite was behind an attempt to spring Grant from prison in Mombasa where he is currently on trial for terrorist offences.
The Kenyan police believe Lewthwaite may have married another Londoner, Habib Ghani, who also joined the terror group in Somalia.
Ghani and an another US-born member of the group, Omar Hammami, were both shot dead during internal feuding at the start of the month.
In June this year Lewthwaite was named by Kenyan police in connection with a grenade and gun attack on the Jericho Beer Garden in Mombas, while customers were watching a Euro 2012 quarter-final match, killing three and injuring 30.
Lewthwaite was born in Northern Ireland after her father, Andy, married Banbridge woman Christine Allen. The family moved to Buckinghamshire in 1995 where their daughter converted to Islam at the age of 17 and changed her name to Sherafiyah. She married fellow convert Germaine Lindsay. She was pregnant when Lindsay took part in the July 2005 bombings in London in which 52 people died. Although not initially suspected, police later discovered that Lewthwaite had a key role in bomb-making and preparing the attack.
Details of last Saturday's bloodbath in Nairobi are still emerging with the expectation that the official death count of 67 will rise substantially. Part of the centre collapsed after an explosion under the roof-top car park. At least 60 people are unaccounted for.
There was still no clear picture of how many terrorists were involved. Sources suggest that up to seven may have been arrested and a similar number killed. The belief that Lewthwaite and others slipped away during the mayhem was underlined the day of the attack in which an eyewitness said he saw a man he described as Arab shooting then concealing his gun and walking out among fleeing shoppers.
Meanwhile, it has emerged that several former Irish Army Rangers are operating in east Africa, where one assisted in rescuing people from the Westgate Mall.
Irish army sources last week said at least six former Irish soldiers are known to be working for security firms operating in east Africa, most thought to be working on anti-piracy operations on board ships passing the Somali coast.
The ex-Army Ranger who last weekend assisted hundreds of people escaping from the shopping mall was alongside a former member of the British Army's Special Air Service (SAS), who runs a company providing security on board ships.
The ex-SAS man has been working in east Africa for several years, local sources say. It is likely that the former Irish soldier is in the same business.
Other former Irish soldiers have been operating in the region for years, some working for private companies and some providing security and logistics for charities operating in the highly volatile areas along the Somali-Kenyan border.
Samantha Lewthwaite was born in Banbridge, Co Down. She converted to Islam as a teenager and is the widow of one of the London suicide bombers. Dubbed the White Widow, mother-of-three is believed to be the mastermind behind the Nairobi Westgate mall massacre which claimed over 70 lives. A 'Red Notice' has been issued by Interpol making her world's most wanted female terror suspect.