The main suspect in a deadly attack on a Kuwaiti Shiite mosque in June confessed in court on Tuesday to being in the jihadist Islamic State group.
Abdulrahman Sabah Saud told the first hearing of the trial of 22 men and seven women that he joined IS just a day before the June 26 suicide bombing that killed 26 people and wounded hundreds.
It was the worst ever attack in the oil-rich Gulf emirate.
Although the public prosecution has not released the official charge sheets, a number of defendants are charged with being in a proscribed group and taking part in the bombing.
Most are also accused of assisting those behind the attack.
Saud, who drove Saudi bomber Fahad al-Qaba'a to the mosque in Kuwait City, was arrested two days after the blast in a hideout owned by two other suspects.
Saud also confessed to transporting an icebox containing the explosives belt used in the attack from near the border with Saudi Arabia.
The icebox was delivered by two Saudi brothers who are now in custody in Saudi Arabia along with a third brother who was arrested in Kuwait.
Tuesday's hearing was held under tight security, with everyone checked before being allowed into the courtroom.
Five defendants are still at large and being tried in absentia.
The seven women present, wearing black abayas and face covers, were allowed to sit with female police guarding them while the male defendants were placed in a metal cage.
Only Saud admitted being in IS: all of the others denied involvement in the bombing or with the jihadist group.
Thamer al-Jadaei, the lawyer for Jarrah Nimer, owner of the car used in the attack, said his client gave the vehicle to Saud to transport charity meals for breaking the fast during the Muslim holy fasting month of Ramadan.
Jadaei also told the court that all members of Nimer's family are Shiites since he is himself a convert.
The women defendants include the wives of both Saud and Nimer.
Those charged are seven Kuwaitis, five Saudis, three Pakistanis, 13 stateless people known as bidoons and another person at large whose identity is unknown.
An IS-affiliated group calling itself Najd Province claimed the bombing and also said it carried out suicide attacks at two Shiite mosques in Saudi Arabia in May.
The extremist Sunni IS considers Shiites to be heretics and has targeted them across the region.
The next hearing in the case was set for Thursday.