Boston: Dzhokhar Tsarnaev has maintained an impassive demeanour throughout his trial. Even as survivors told of the carnage he inflicted at the 2013 Boston Marathon, and family members described how he killed their loved ones, he barely seemed to flinch.

But on Monday, as his aunts and other relatives from Russia testified on his behalf, in their native tongue, he reached for a tissue, dabbed his eyes and began to weep.

The relatives were crying too, some sobbing outright. For many, Monday was the first time they had seen him since his family left Russia in 2002, and it was likely to be the last: After the trial, he will either be executed, or locked behind bars by himself for 23 of 24 hours a day for the rest of his life.

One aunt, Patimat Suleimanova, in her mid-60s, was crying so uncontrollably, she was gasping for breath, even before she began to testify. Judge George A. O’Toole junior suggested that the defence call another witness so she could leave the stand and compose herself. It was at that point, as the woman, wrapped in a shawl, her grey hair mostly in a bun, trundled off, that Tsarnaev, 21, began to cry and wipe his face.

It was an unusual display of emotion all around as the defence team sought to persuade the jury to spare Tsarnaev’s life.

Last month, in the first phase of the trial, the jury convicted him of all 30 charges against him in connection with the bombing of the marathon, which killed three people and injured 264 others. In this, the penalty phase, the government is arguing that he be sentenced to death, and the defence wants him sentenced to life in prison without parole.

As it argued for execution, the prosecution called Tsarnaev unrepentant and said he had no remorse for the lives he took and the mayhem he caused.

The defence has never suggested that he did feel remorse; in fact, it has said nothing about his feelings. His weeping was his first visible reaction to the trial, beyond slouching in his chair and appearing bored.

Instead, his lawyers have sought to humanise him, building a narrative that casts him as an easy-going youth, more of a go-along type than someone with an independent will or any particular ambition or agenda, in keeping with the stoner profile he developed as a college student.

Witness after witness has spoken of Tsarnaev’s sweet nature. Many said he had a powerful effect on women, particularly older women, melting their hearts and entrancing them with his smile.

His cousin, Nabisat Suleimanova, who is in her early 40s, described him through an interpreter as a “wunderkind” and said he was so warm and caring, “one wanted to hug him and not let him go.” She said his smile brought out the maternal instincts in another, otherwise stern aunt.

“When Jahar appeared,” she said, using his Americanised nickname, “she changed drastically, she would even let him urinate in the sink in the kitchen.”

He was still learning English when he entered third grade in Cambridge, but he worked hard enough to skip fourth grade.

Tracey Gordon, one of his teachers, described him last week on the stand as “super kind, really smart, very quick to learn, a very hard worker”. Gordon recommended him for a program in which he would help mediate other students’ disputes.

Becki Norris, a former teacher ho testified last week that his teachers “all loved him,” wrote on Facebook that “I still love him,” even though he did “unfathomably horrible things.”

On Monday, another aunt, Shakhruzat Suleimanova, testified that Tamerlan and Dzhokhar were “so good, they wouldn’t hurt a fly.”

But William Weinreb, the lead prosecutor, criticised the portrayal of the convicted bomber as a kind and endearing boy. “But you’d agree that the bombing of innocent people is not an act of kindness?” he asked Raisat Suleimanova, a cousin, drawing an objection from the defence that shut down that line of questioning.

She had testified that as a boy, Dzhokhar had cried during the movie “The Lion King” when Mufasa, the father lion, dies. Weinreb pressed her: “Would you agree that someone who cries at the death of a cartoon character but is indifferent to the suffering of hundreds of people “

He was cut off before he could finish his question, but he got his point across.