Story highlights Dzhokhar Tsarnaev's parents play parts of a phone call with him on ITN's Channel 4

The parents insist their sons, Dzhokhar and Tamerlan Tsarnaev, are innocent

Tamerlan Tsarnaev was killed in a police shootout and was run over by his brother

Inside their dark, barren home in Dagestan, Zubeidat and Anzor Tsarnaev finally hear the voice they've been longing to hear for weeks.

It's the voice of their only surviving son, Dzhokhar . To the outside world, he's suspected of helping to launch a gruesome attack at the Boston Marathon that killed three people and maimed dozens more.

But to the Tsarnaevs, Dzhokhar is an innocent teen who has been victimized by the American justice system.

In an exclusive interview with CNN affiliate ITN , Zubeidat Tsarnaev plays a recorded phone call with her 19-year-old son. It's their first conversation since Dzhokhar Tsarnaev was shot and arrested in April.

Zubeidat Tsarnaev asks her son whether he's in pain.

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"No, of course not. I'm already eating and have been for a long time," Dzhokhar responds in the call from a prison hospital recorded last week. "They are giving me rice and chicken now. Everything's fine."

Dzhokhar's apparent calm surprises his mother.

"I felt like he would scream, you know, like, 'What's going on?'" Zubeidat Tsarnaev tells ITN's Channel 4. "Instead, he was just calming me down."

The parents insist their sons, Dzhokhar and 26-year-old Tamerlan, weren't responsible for the Boston bombings on April 15.

"It is terrible what happened, you know, but I know that my kids did not do it," Zubeidat Tsarnaev says.

After a wild police chase, Tamerlan Tsarnaev died in a shootout with police. He was also run over by his fleeing brother.

The family says Dzhokhar Tsarnaev was supposed to visit Dagestan the same week as the bombing.

"We were waiting for you on the 18th at home," Anzor Tsarnaev tells his son in the phone call. "Not in our worst nightmares did we imagine this."

The father says he doesn't think his son understands what has happened to him.

"I understand. I'm just someone in shock because justice has vanished," Anzor Tsarnaev says. "There is no justice. It's impossible to understand what happened."

Anzor Tsarnaev tells his son they will meet again in heaven.

"We're going to be together," he says.