According to the statement released by the governor's office, bomb disposal experts found out that the suicide bomber detonated some 6 kilograms of TNT explosives as well as a hand grenade during the attack.
The suicide bomber, identified as Ecevit Şanlı, a member of the far-left terrorist Revolutionary People's Liberation Party/Front (DHKP/C), killed himself and a Turkish security guard in the attack.
The statement confirmed that the attacker was sent to jail in 1997 spent four years in prison on terrorism charges before being released for a brain disorder contracted while on hunger strike.
The 40-year-old bomber killed himself and a Turkish security guard on Friday in an attack Turkish officials blamed on domestic leftist militants. It was the second deadly assault on a US diplomatic post in five months.
The statement said Åžanli was arrested in 1997 for membership in the DHKP/C, and took part in a major hunger strike that led to the deaths of dozens of inmates.
The US flag at the embassy flew at half-staff and already tight security was increased. Police sealed off a street in front of the security checkpoint where the explosion knocked a door off its hinges and littered the road with debris. Police vehicles were parked in streets surrounding the building.
Officials said the bomber was arrested in 1997 for alleged involvement in attacks on the police headquarters and a military guesthouse in İstanbul and jailed on charges of membership in the group. While in prison awaiting trial, he took part in a major hunger strike that led to the deaths of dozens of inmates, according to the statement from the Ankara Governor's Office. The protesters opposed a maximum-security system in which prisoners were held in small cells instead of large wards.
Şanlı was released in 2002 after being diagnosed with Wernicke-Korsakoff syndrome, a malnutrition-related brain illness that affects vision, muscle coordination and memory and that can cause hallucinations. Şanlı fled Turkey after his release and was wanted by Turkish authorities, the statement said. He was convicted in absentia in 2002.
Interior Minister Muammer Güler said on Saturday that police found out that the suicide bomber entered Turkey illegally with a fake identity.
Officials had earlier said that the bomber detonated a suicide vest at the checkpoint on the outer perimeter of the compound.
The guard who was killed was standing outside the checkpoint. Didem Tuncay, a Turkish TV journalist, was seriously wounded and two other guards had lighter wounds
The attack drew quick condemnation from Turkey, the US, Britain and other nations, and officials from both Turkey and the US pledged to work together to fight terrorism.
It was the second deadly assault on a US diplomatic post in five months. On Sept. 11, 2012, terrorists attacked a US mission in Benghazi, Libya, killing US Ambassador Chris Stevens and three other Americans. The attackers in Libya were suspected to have ties to Islamist extremists, and one is in custody in Egypt.