Rauf Arashukov is accused of being involved in the 2010 killing of two people and other crimes, said the Investigative Committee of Russian Federation.
Raul Arashukov was arrested as well later in the day on charges of embezzlement.
A Russian lawmaker was arrested Wednesday in the middle of a parliament session in connection with two murders committed eight years ago, an official and news reports said.
Russia's Investigative Committee believes Arashukov is involved in the murders of Karachay-Cherkessia presidential advisor Fral Shebzuhov and the deputy leader of state's youth movement, Aslan Zhukov.More news: Samsung Galaxy S10 and Galaxy S10
A video released by the Investigative Committee showed Arashukov, in handcuffs, being brought to its headquarters for questioning.
Investigators said Mr Arashukov, who represents the minority region in the Upper House, was having difficulties with the Russian language and had asked for an interpreter.
Earlier, the father and the cousin of the member of the Federation Council were detained.
Rauf Arashukov was on the senate floor when police officers entered and read out a warrant, according to senate speaker Valentina Matviyenko.More news: Europeans open new trade channel to Iran
The 32-year-old politician tried to escape by running upstairs, but was ordered by the chairwoman to return to his seat in an "icy voice", according to witnesses. "I told him to stay put because according to current regulations he had the right to speak and explain himself", she said.
A former municipal lawmaker and district head in Karachai-Cherkessia, Arashukov became a member of the Federation Council in September 2016 and represented the executive branch of the regional government in the upper house.
Arashukov denies the accusations, his lawyer was quoted by RIA news agency as saying. Petrenko reiterated that these criminal cases are being investigated by the Main Investigative Directorate of the Russian Investigative Committee.
Later on Wednesday, investigators announced that Arashukov's father, Raul, who is a top manager at gas company Gazprom, has been detained on suspicion of embezzling 30 billion rubles' ($455 million) worth of gas supplies.More news: Liverpool boss Jurgen Klopp explains Leicester snow controversy