The man behind one of the deadliest bombings in recent years was a former soldier whose hometown was raided by US special forces two months ago, officials in Somalia said.
More than 300 people were killed and hundreds more injured when two truck bombs exploded in the capital, Mogadishu.
Scores of people are still missing after the attack, the deadliest in the country’s history, and officials have said the death toll could still rise.
Somalian investigators told the Guardian the attack may have been motivated by revenge, following a joint US-Somali operation in August in which 10 civilians, including three children, were killed.
The raid, carried out in the town of Bariire – a stronghold of al-Shabaab – allegedly prompted local tribal elders to call for revenge against the Somali government and its allies.
The bomber who carried out last week’s attack was from the community targeted in the August raid.
Investigators have also established that both vehicles used in the Mogadishu bombing appear to have come from Bariire, officials said.
The blasts struck two busy areas in the heart of the city on Saturday 14 October, killing at least 320 people.
Police said a truck bomb exploded outside the Safari Hotel at the K5 intersection, an area home to government offices, restaurants and kiosks.
Two hours later, a separate blast hit the Medina district.
President Mohamed Abdullahi Mohamed declared three days of mourning in the aftermath of the bombing and joined thousands of people who donated blood to hospitals.
“I am appealing all Somali people to come forward and donate,” he said.
The attack is the deadliest since the Islamist militant group al-Shabaab began an insurgency in 2007.
Although no group has claimed responsibility, al-Shabaab – which is allied to al-Qaeda – carries out regular attacks in Mogadishu and other parts of Somalia.
This latest attack has cast scrutiny on US efforts to eliminate al-Shabaab.
Earlier this year, President Donald Trump approved the expansion of military operations against al-Shabaab, including air raids.
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