The suspects' uncle, speaking to reporters in Montgomery, Maryland, said he was "ashamed" of Dzhokhar and Tamerlan Tsarnaev.
"Of course we're ashamed, they are children of my brother, who had little influence on them," he said.
"They've never been in Chechnya. Chechens are peaceful people."
"I say Dzhokhar, if you are alive, turn yourself in and ask for forgiveness."
"He put shame on the entire Chechen ethnicity."
Detectives in Boston are looking further afield as they piece together their case against Marathon suspect Dzohkhar Tsarnaev.
The uncle of Boston bombing suspect Tamerlan Tsarnaev described his recent visit to Dagestan in Russia and his great shock at the attacks.
Both men were enrolled in a school in Dagestan, a neighbouring region that was drawn into Chechnya's violence during the 1990s.