Earlier in June, they were sentenced by a US federal judge to 3.5 and six years in prison, respectively, for obstructing the investigation into the April 2013 bomb attack carried out by Tsarnaev brothers. According to the prosecution, the two men collected a backpack containing evidence from Dzhokhar Tsarnaev’s dorm room at the University of Massachusetts Dartmouth and threw it in the trash.
"The consent of the United States is necessary for the transfer of the convicts to their homeland. Otherwise, they will serve their sentences where they were convicted," Iogan Merkel was cited by Novosti, Kazakhstan news agency.
On Wednesday, Dzhokhar Tsarnaev addressed victims of the bombing for the first time after a US judge sentenced him to death for his role in the 2013 Boston marathon bombing that killed three people and injured more than 260. His brother Tamerlan was killed in a police shootout in the days following the attack.