Nairobi - Four gunmen who attacked a Nairobi shopping mall in September came to Kenya about four months earlier and some had exercised at a gym in an area of the Kenyan capital popular with Somalis, Western officials with knowledge of the investigation said.
Kenyan police, with help from several Western nations, are piecing together events leading up to the assault on Westgate mall, which killed at least 67 people and which highlighted the reach of Somalia's al-Qaeda-aligned Islamist group al-Shabaab.
Tracking down where the gunmen stayed and how they spent their time before the strike has led to a suburb of Nairobi known as "Little Mogadishu" because of its large Somali population and a small gym on the first floor of Eastleigh Mall, a shopping complex in the area.
"We know where they lived. We know the gym several of them used. We know when they acquired the vehicle," said one of the Western officials, who spoke on condition of anonymity.
He said all four gunmen, who had spent time together in Somalia before the attack, had crossed into Kenya overland in June. "They came in through a common entry point," the official said, without saying where on Kenya's border that was.
A trainer at the New Andalus Gym, where the schedule posted at the door is written in both English and Somali, said criminal investigators had visited twice about two weeks ago. He said the officers said they had information the gunmen worked out there.
"They just asked us if we had any information about those people," Moses Baraza said at the gym, a single, steamy room packed with treadmills, weights and other exercise machines where about 30 men were working out on Monday evening.
The officers showed pictures, checked a register and spoke with the cashier sitting in a small booth at the gym, where membership costs 1 800 shillings a month. He added the officers said they had found a gym receipt at Westgate mall.
But Baraza, who said most clients were originally from Somalia, added he did not recognise any faces he was shown because it was difficult to remember individuals at a gym with a high turnover of members. Few stay longer than a month or two.
Although the Kenyan authorities initially blamed a group of 10 to 15 gunmen for the attack, Western officials and Kenyan police said they now believed only four men with AK-47 assault rifles and grenades had carried out the assault.
"We are now confident that we know the true identities of the four attackers," said a second Western official, adding that they were all believed to be Somali nationals.
A source in Kenya's Anti-Terror Police Unit told Reuters the identities of two of the four attackers had been established, but said they were still working on confirming the two others.
The Western officials only referred by name to two of the attackers, Mohamed Abdinur Said and Hassan Mohamed Dhohullow, who have already been listed on court document charging four other Somalis accused of helping the gunmen at various stages.
Dhohullow has previously been identified as having Norwegian citizenship as well. Investigators are examining any other international links, the Western officials said, adding there was no indication any had visited Britain or the United States.
Highlighting concerns that Somalia has become a launchpad for global operations by al-Shabaab, US, British, Israeli and other foreign investigators have been helping the Kenyan probe.
"The evidence continues to point to the fact that the attackers were linked to al-Shabaab. There are questions that still remain about which specific element or elements of al-Shabaab were involved," said the second Western official.
"It is crucial that we ... understand the full network."