Lawyers representing accused Boston Marathon bomber Dzhokhar Tsarnaev in his upcoming death penalty trial discussed a key argument in their defense strategy during a hearing on Monday.

Just days before opening arguments began in the high-profile case, the defense team discussed the theory that Tsarnaev participated in bombing the 2013 Boston Marathon because he was dominated and motivated by his now-deceased older brother, Tamerlan.

The 21-year-old suspected terrorist is facing capital punishment for allegedly detonating two pressure-cooker bombs at the finish line of the Boston Marathon on April 15, 2013 with his brother. The bombs killed three people and injured 264 others. In addition, federal prosecutors say he and Tamerlan also fatally shot a Massachusetts Institute of Technology police officer three days later. Tamerlan was then killed on April 18, 2013 during a police shootout.

According to the defense, Tsarnaev, who has pleaded not guilty to all charges, was controlled by his older and domineering sibling.

"The lead conspirator, the person who started all this and without whom the Boston Marathon bombing would never have occurred, the older brother, is dead," defense attorney David Bruck told U.S. District Judge George O'Tool, adding "that presents a problem for the government's request for the death penalty," reports Reuters.

"A large part of the motive may have been the defendant's love for, admiration of, submissiveness to, his older brother," Bruck continued.

However, prosecutors said that argument should not be presented until the sentencing phase of the trial.

Defense lawyers "want to advance the theory of the co-conspirator's culpability in the liability phase. It's simply not relevant," said Assistant U.S. Attorney Aloke Chakravarty.

The two sides also argued over how to present evidence from the boat where Tsarnaev was found hiding before he was taken into custody by police officials on April 19, 2013. The defense maintained that the jury should have the opportunity to examine the full boat, which was riddled with bullets, while prosecutors say only certain parts of the boat should be presented as evidence, including the handwritten notes he engraved inside of it.

"We Muslims are one body. You kill one of us, you hurt us all," read one of the lines found in the boat.

"The government is killing our innocent civilians but most of you already know that," another portion of the message said, reports ABC News.

In addition, defense attorney Miriam Conrad argued the jury should not view fully-body images of the victims on the grounds that they are too gruesome. Instead, she said that the pics should be cropped.

"They are horrific, they are disturbing, they do not go to any disputed question of fact in this case," said Conrad, reports The Wall Street Journal.

On the other hand, Assistant U.S. Attorney Nadine Pellegrini said the full photos are need to help the government prove its case about the device that was used in the bombing.

"Full body is requested because they are injured everywhere on their bodies," said Pellegrini. "They are gruesome and graphic because they show the deaths of three young people by what we contend was a bomb."

The presiding judge in the case did not issue an immediate ruling on any of the issues.

Related