Lawyers for Boston Marathon bombing suspect Dzhokhar Tsarnaev said Wednesday that understanding Tsarnaev’s family is key to their case, offering a glimpse of the defense strategy as they prepare to defend him against charges that carry the possibility of the death penalty.

Tsarnaev’s lawyers have previously indicated that they are planning to argue that he was influenced by his 26-year-old brother, Tamerlan Tsarnaev, who authorities say was his co-conspirator.

On Wednesday, the defense suggested that they will delve deeper into the dynamic of the Tsarnaev family, including the relationships the brothers had with their two sisters and their parents.

Tamerlan Tsarnaev was killed in a shootout with police several days after the April 15, 2013, bombing. Dzhokhar is awaiting trial on 30 federal charges.

Attorney David Bruck focused on Tsarnaev’s family while asking a judge to lift special restrictions on Tsarnaev in prison, including FBI monitoring when his two sisters visit him.

“I don’t think there is anybody that has seen what has unfolded in the last year and a day who doesn’t understand that if the government’s indictment is true — this is about a family — and the search for an understanding of what happened is in large measure a story of this family and the relationships between people in it,” Bruck said.

Bruck said the presence of the FBI agent during the sisters’ visits hurts the defense team’s ability to observe Tsarnaev’s interactions with them.

Assistant U.S. Attorney Nadine Pellegrini argued that Tsarnaev “felt free to say whatever he wanted,” despite the presence of the FBI agent and a member of the defense team.

U.S. District Judge George O’Toole Jr. did not issue a formal ruling but indicated he will ease the restrictions when Tsarnaev’s sisters visit. He said he may exempt the visits from monitoring by the FBI agent or find someone to monitor the visits who is not part of the prosecution team.

Separately, O’Toole rejected a prosecution request to limit Tsarnaev’s access to autopsy photos of the three people killed in the bombing and an MIT police officer authorities say was killed by the Tsarnaev brothers days later.

Prosecutors also agreed to a request from Tsarnaev’s defense lawyers to turn over immigration files of the entire Tsarnaev family. The family, ethnic Chechens who lived in the former Soviet republic of Kyrgyzstan and the Dagestan region of Russia, settled in the United States more than a decade ago.

The defense renewed its request for prosecutors to turn over any information they have on the alleged involvement of Tamerlan Tsarnaev in a 2011 triple homicide in Waltham.

Assistant U.S. Attorney William Weinreb said the documents are not relevant because there is no evidence that Dzhokhar knew about his brother’s alleged role in the slayings. He said releasing the details could jeopardize an ongoing state investigation into the slayings.

O’Toole said he would review the documents before deciding whether the defense is entitled to them.

(AP)