A brother of the late organizer of the 2018 killing of four foreign cyclists in Danghara district of Khatlon province has been handed an additional 20 years in prison after the Supreme Court found him guilty of calling inmates to stage riots that claimed dozens of lives in 2019, according to Radio Liberty’s Tajik Service.

Sources close to the Supreme Court of Tajikistan told RFE/RL’s Tajik Service on September 1 that the trial of Bakhtiyor Abdusamadov was held behind closed doors and that his case was related to the deadly prison riot in Vahdat Township near Dushanbe in May 2019.

Abdusamadov's mother, Gulchehra Shodmonova, told RFE/RL that her son had denied any involvement in the riot in which 32 people died, including three prison guards.

The 39-year-old Bakhtiyor has been serving his 16-year prison term since 2009 for being a member of a criminal group involved in illegal border-crossing activities.

His brother Hussein Abdusamadov, who was sentenced to life in prison for his role in the killing of four foreign cyclists in the Danghara district in July 2018, died while incarcerated in March.

Hussein Abdusamadov was the sole survivor of a group of attackers who killed the Western cyclists.

The four cyclists -- two Americans, a Dutch national, and a Swiss national -- were killed on July 29, 2018, when attackers plowed their vehicle into their group on a road and then stabbed some of them.

Two other foreign cyclists survived the attack, which occurred about 150 kilometers south of Dushanbe.

Four suspects in the attack, Zafarjon Safarov, Asomuddin Majidov, Jafariddin Yusupov, and Asliddin Yusupov, were killed by Tajik security forces.

Hussein Abdusamadov, who was named the group's leader, survived, and was found guilty of murder in November 2018.

The Islamic State (IS) terror group claimed responsibility for the attack shortly after it occurred and released a video showing five men -- at least some of whom appeared to resemble those identified by Tajik officials as suspects killed in a confrontation with security forces -- pledging allegiance to the leader of IS.

The Tajik government, however, rejected the claim and instead blamed followers of the Islamic Renaissance Party of Tajikistan (IRPT), a political party that was banned by the Tajik authorities in 2015.

The leadership of the IRPT has denied involvement and called the authorities' claims "shameless and illogical slander."