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Somalia is marking the first anniversary of one of the world's deadliest attacks since 9/11, a truck bombing in the heart of Mogadishu that killed well over 500 people.

As people gathered on Sunday at a new memorial with a minute of silence, a man accused of orchestrating the bombing was executed by firing squad. Capt. Mumin Hussein, deputy prosecutor general of the Somali military court, confirmed the execution of Hassan Aden Isaq, the first under the country's Somali-American President Mohamed Abdullahi Mohamed.

Memories of the bombing are still raw in a country that has faced decades of deadly warlord-led chaos and attacks by the al-Qaida-linked al-Shabab extremist group. The Oct. 14, 2017 bombing was so devastating that al-Shabab never claimed responsibility amid local outrage.

The newly arrived U.N. envoy to Somalia, Nicholas Haysom, on Sunday called it "the deadliest ever terrorist attack in Africa, and such terrorist attacks amount to a war crime."

"In my mind, it feels like it has happened just yesterday," said Sadiya Mohamed, a 49-year-old who lost her eldest son. He is among hundreds of people still missing. "I can barely get sleep since that dark day. He was everything for us," she said.

Somalia's government has declared Oct. 14 as a national day to remember victims of all "terrorist" bombings across the Horn of Africa nation.

On Sunday, the president traveled to the coastal town of Marka to mark the anniversary with a military brigade formed by young men who volunteered for service after the attack, presidential spokesman Abdinur Mohamed told The Associated Press. The brigade is named after the bombing.

Somalis now look to the future with a mixture of sorrow and hope.

Many believe the global attention to the attack and outpouring of grief should bring much-needed assistance for the fragile central government and security forces, who in the next few years are expected to take over the country's security from African Union peacekeepers.

"That was a big test for the international community's seriousness in helping Somalia to move forward," said Ahmed Mohamed, a former lawmaker.

For many of the victims' loved ones, Sunday was simply a day to grieve.

"Imagine living with the reality of not having your father dead or alive," said Mohamed Sheikh, a 17-year-old rickshaw driver whose father is among the missing. "That memory keeps haunting me each day and night."

The bombing shattered one of Mogadishu's busiest business districts. Reconstruction has begun but many buildings in the area still lay in ruins.

Most of those killed were civilians going about their daily lives when the truck that had been trying to force its way through heavy traffic exploded.

Security officials have said they had advance warning about an incoming vehicle but had no idea about the large amount of explosives it carried.

"We had been trailing the car bomb before it was detonated but he sped through a traffic jam and unfortunately reached the site," said Abdullahi Sanbalolshe, Somalia's former intelligence chief.

Amid the shock of the blast, hospitals and officials pleaded for Mogadishu residents to donate blood. Many pushed cultural hesitations aside and got in line.

Some survivors say the attack changed their lives forever.

"I regained consciousness and found myself on a hospital bed with serious burns on nearly all of my body," said Yusuf Ahmed, a shopkeeper who lost his wife in the blast.

The 35-year-old father of four now raises their young children. "She was the light and the only helper of my life," he said. "My life changed for the worst since I lost her."

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