MOSCOW — A member of the Kremlin’s advisory council on human rights said on Wednesday that the main suspect in the shooting death of a high-profile opposition figure was most likely forced to confess under duress, and that his two cousins in detention had been tortured.

After visiting the three Chechens, who were among five suspects imprisoned on Sunday in Lefortovo Prison in Moscow, Andrei Babushkin, a rights activist, said that the men had suffered multiple injuries after their arrest.

In a summary of the visit posted on the council’s website, Mr. Babushkin also reported that another man arrested at the same time as Zaur S. Dadayev, the main suspect, had disappeared and said that he had asked Russia’s top law enforcement agency to account for his whereabouts.

The 40-member presidential council — officially the Council Under the President of the Russian Federation for the Development of Civil Society and Human Rights — has a reputation for a certain degree of independence and a real interest in some human rights issues like the treatment of prisoners. Not all members sign every statement, but rights experts said overall committee members do serious, trusted work.