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 / Updated  / Source: NBC News

A relative of convicted Boston Marathon bomber Dzhokhar Tsarnaev was denied entry to the United States last month when he arrived from Russia for the penalty phase of the trial, sources with knowledge of the matter told NBC News.

The family member was turned around at Logan International Airport and sent right back home to Russia 10 days ago because he did not want to adhere to security measures imposed on the family members, the two sources confirmed, speaking on condition of anonymity due to the ongoing trial.

These measures included ankle bracelets and law enforcement monitoring.

The sources did not identify the relative. But one source said the relative had been uncooperative in the past during the government's investigation of Tsarnaev family following the April 15, 2013, bombing, which killed three and injured over 200 others.

The FBI declined to comment on anything related to the Tsarnaev family.

A Customs and Border Patrol‎ spokesperson said the agency could not comment on specific individuals. The spokesperson issued a statement that says, in part, "under ‎U.S. immigration law, applicants for admission bear the burden of proof to establish that they are clearly eligible to enter the United States. In order to demonstrate that they are admissible, the applicant must overcome ALL grounds of inadmissibility."

The relatives who made it for the trial are being held at an undisclosed location in the greater Boston area, the sources said.

On Thursday, when some of them were expected to testify, they were transported in three separate cars driven by law enforcement, all taking separate routes and using an underground garage in the FBI's headquarters in downtown Boston in an apparent attempt to avoid media helicopters.

The relatives' testimony was postponed until Monday after a juror became ill.

As many as five family members are expected to testify as the defense continues their presentation and testimony in the death penalty phase of Dzhokhar Tsarnaev's trial Monday.

—Tom Winter and Jon Schuppe

A courtroom sketch shows Boston Marathon bombing suspect Dzhokhar Tsarnaev (L) and his defense team as the verdict is read at the federal courthouse in Boston, Massachusetts April 8, 2015. Tsarnaev was found guilty on Wednesday of the 2013 Boston Marathon bombing that killed three people and injured 264 others, and the jury will now decide whether to sentence him to death.JANE FLAVELL COLLINS / Reuters