BALTIMORE (WJZ) — Emotional testimony in a Boston courtroom as survivors of the marathon bombing face their attacker. A jury will decide if Dzhokhar Tsarnaev lives or dies.

Tuesday, one of two Maryland sisters injured in the blasts took the stand.

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Meghan McCorkell has more on her testimony.

Nicole Gross was standing right next to her sister, Erika Brannock, when the bombs exploded. Tuesday, she testified in the first day of the penalty phase of the trial.

Cell phone video played in court shows the chaos and horror in the seconds after two bombs went off near the finish line of the Boston Marathon.

Prosecutors arguing for the death penalty showed the jury a photo of Dzhokhar Tsarnaev making an obscene gesture at a security camera, saying he was “determined to be America’s worst nightmare.”

Waiting for their mother at the finish line, Erika Brannock and Nicole Gross were thrown to the ground by the blast.

Gross told the jury: “My right quad was wide open. My foot was hanging by what felt like threads. I just screamed for someone to save me or hear me.”

A picture of Gross made headlines around the world.

She said: “I saw my sister and she was laying down and my eyes were closed. I was not sure what was going to happen to me.”

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“We were right on top of each other when it happened, when the bomb went off,” said Gross in 2013.

Gross has undergone nearly a dozen surgeries. Her sister, Erika Brannock, a Towson preschool teacher, lost part of her left leg.

“I just remember myself slipping away,” said Brannock.

Brannock recently recounted her memories of being rushed into an ambulance.

“I remember hearing we have two criticals, we have one amputee,” she said.

Four people died in the bombings and aftermath. Surviving bomber Dzhokhar Tsarnaev is convicted on 30 counts.

Now, a 12 juror panel will decide if the destruction he caused warrants the death penalty.

Reporters inside the Boston courtroom tell WJZ they did not see Erika Brannock there Tuesday. It’s unclear if she will testify.

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Tsarnaev’s defense is expected to present its case to the jury sometime next week.