The mother of the sole survivor of a group of attackers who killed four Western cyclists in the Danghara district in 2018 has raised questions about the death of her son in prison.

Gulchehra Shodmonova, mother of Hussein Abdusamadov, who was considered the group's leader, told RFE/RL on March 3 that, after her son's burial, she was told by authorities that the cause of death was kidney failure.

Shodmonova said she visited her son several days before his death in prison, where he was serving a life sentence for his role in the killing of the foreign cyclists on in Danghara in July 2018, and that he looked good and had no complaints about his health.

"They say he got sick on March 1 and died the next day.  If they consider themselves true Muslims, they should tell us how and what exactly he died of," Shodmonova told RFE/RL, adding that there were no traces of violence on her son's body.

Mansourjon Umarov, chief of the Main Directorate at the Tajik Justice Ministry's Penitentiary Service, told RFE/RL on March 3 that Abdusamadov's body bore no signs of violence, adding that investigations had been launched into the death of what he called “a dangerous terrorist.”

Four cyclists -- an American woman and man, a Dutchman, and a Swiss man -- 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.

Abdusamadov 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.