Boston (CNN) Jurors resumed deliberating Thursday morning whether Boston Marathon bomber Dzhokhar Tsarnaev should spend the rest of his life in prison or be executed for his role in killing four people and wounding dozens more.

The jury was given the case Wednesday afternoon following attorneys' closing arguments. The prosecution told jurors Tsarnaev was a remorseless terrorist worthy of the death penalty, while the defense said he was repentant and deserved to be spared.

"The defendant knew what kind of hell was going to be unleashed," prosecutor Steve Mellin said.

Defense attorney Judy Clarke countered: "We're asking you to choose life. Yes, even for the Boston Marathon bomber."

U.S. District Court Judge George O'Toole sent the jury out shortly after 4 p.m. Wednesday. "The importance of your deliberations is obvious," he said. About an hour later, jurors were sent home for the night.

"You have a long way to go," the judge told them before reminding them to avoid any outside information or discussion about the case overnight.

Tsarnaev, who is 21, was convicted in April of 30 counts; 17 of them carry a possible death sentence. He was found guilty of conspiring and detonating weapons of mass destruction at a public event as an act of terrorism resulting in death.

Jurors will complete a 24-page questionnaire that asks them to weigh "aggravating" factors presented by the prosecution and "mitigating" factors advanced by the defense before making a final decision on life or death for each of the 17 counts.

O'Toole earlier reminded jurors they have to be unanimous to return a death sentence and that no juror is under any obligation to choose death.

Hoping to spare Tsarnaev's life, defense attorney Clarke told jurors in her closing argument that her client has shown repentance and is "not the same angry young man the prosecution has described to you."

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"He'll have no glory or stature that martyrdom will bring. His name will fade from the headlines. It will fade from the news altogether and those who so desperately no longer want to be reminded of him."

Clarke made her plea shortly after the prosecution told jurors Tsarnaev was a terrorist whose actions "have earned him a sentence of death."

Prosecution: 'What terrorism looks like'

In his closing argument, prosecutor Mellin showed gruesome images to remind jurors of the carnage unleashed on April 15, 2013 , stating: "This is what terrorism looks like."

Mellin then named the three people killed in the bombings carried out by Tsarnaev and his older brother, Tamerlan Tsarnaev, who was killed in a shootout with police.

Martin Richard , 8: "Bleeding in agony, while his mother bends over, injured in one eye, begging him to live."

Lingzi Lu , 23: "Screaming in pain while she dies in that street."

Krystle Campbell , 29: "Burned all over her body, filled with shrapnel, with smoke coming out of her mouth."

He implored jurors to remember the others in the crowd or running that day who stared "in shock at their mangled and ruined limbs."

"It's hard to think of a better place to murder people than the Boston Marathon if you want to make a statement [that] you think Americans are in need of punishment," Mellin said.

The prosecutor told jurors not to forget about the fourth person killed by the Tsarnaev brothers. Sean Collier , a 27-year-old MIT security officer, was shot at point-blank range days after the bombing.

"Killing a police officer makes all of us more vulnerable."

He especially cited the vulnerability of Martin Richard, who weighed less than 70 pounds. "Can there be anybody more vulnerable than a little boy next to a weapon of mass destruction?" Mellin asked.

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"The defendant placed that bomb on the ground, so the smaller the victims were the more exposed they were to that shrapnel."

The entire Richard family was standing there, with Martin's mother, Denise Richard , suffering grave wounds and his younger sister, Jane, having one of her legs blown off.

"This defendant blinded their mother, maimed their 6-year-old daughter and blew apart their 8-year-old son in front of the father."

Mellin beat back at the defense portrayal of Tsarnaev as a good-natured kid who fell prey to his older brother and followed his orders.

"All murderers start out as cute children, but sometimes the cute children grow up to be bad people," Mellin said. "Tamerlan Tsarnaev was not his brother's master. They were partners in crime and brothers in arms."

He concluded his argument by saying "a death sentence is not giving him what he wants. It's giving him what he deserves."

"After all of the damage and carnage and fear he has caused, the right decision is clear. The only sentence that will do justice in this case is the sentence of death."

Defense: Blame the brother

In her closing argument, Clarke blamed the older brother, Tamerlan , for the radicalization of a once promising, hard-working kid.

"The story of Jahar cannot be told without knowing the story of Tamerlan," Clarke said. "How does this good kid, this youngster, this young man who was described as gentle by friends and family and teachers do this? How does this happen?

"If you expect me to have an answer, a simple clean answer as to how this could happen, I don't have it," the defense attorney said. "I can tell you this. Jahar Tsarnaev is not the worst of the worst. And that is what the death penalty is reserved for -- the worst of the worst.

Photos: Boston Marathon bombing evidence Photos: Boston Marathon bombing evidence A jury condemned Dzhokhar Tsarnaev to death on Friday, May 15, for his role in killing four people and wounding hundreds more in the 2013 Boston Marathon bombings. See photos that were released as evidence in his trial. Hide Caption 1 of 35 Photos: Boston Marathon bombing evidence This undated photo of a young Tsarnaev with his brother, Tamerlan, was shown by the defense in the sentencing phase of the trial. Tamerlan died after being shot by police and run over by a car driven by his brother in the massive manhunt that followed the bombings. Hide Caption 2 of 35 Photos: Boston Marathon bombing evidence Katie Russell met Tamerlan Tsarnaev at a nightclub and dropped out of college to marry him. Her mother, Judith Russell, testified that Tamerlan came between Katie and her family and that Katie became isolated. She eventually converted to Islam and changed her name to Karima Tsarnaeva. She was the breadwinner. But when company came for dinner, she cooked, served the men and then retired to another room. Hide Caption 3 of 35 Photos: Boston Marathon bombing evidence This collection of photos of Dzhokhar Tsarnaev in his wrestling days was introduced by the defense. Hide Caption 4 of 35 Photos: Boston Marathon bombing evidence This photo of Tamerlan Tsarnaev, recovered from his computer, was shown during the sentencing phase. Hide Caption 5 of 35 Photos: Boston Marathon bombing evidence This image shows victims' positions in the crowd prior to the Boston Marathon bombings on April 15, 2013. Hide Caption 6 of 35 Photos: Boston Marathon bombing evidence Tsarnaev "flips the bird" in a jail cell during his first arraignment on July 10, 2013. The image was presented to jurors in the sentencing phase of his trial. Hide Caption 7 of 35 Photos: Boston Marathon bombing evidence Tsarnaev poses in front of a black standard adopted by various militant Islamist groups in this Instagram photo that was entered as evidence. Hide Caption 8 of 35 Photos: Boston Marathon bombing evidence Prosecutors say Tsarnaev was a self-radicalized jihadist who pored over militant writings, including the article "How to Build a Bomb in the Kitchen of Your Mom." It was found on his laptop and other devices, part of a full-edition download of Inspire magazine, a glossy English-language propaganda tool put out by al Qaeda in the Arabian Peninsula. Hide Caption 9 of 35 Photos: Boston Marathon bombing evidence This Russian manual on how to fire a handgun was found in the apartment where Tsarnaev's brother, Tamerlan, lived. Tamerlan Tsarnaev was killed in a shootout with police in Watertown, Massachusetts, on April 19, 2013. Hide Caption 10 of 35 Photos: Boston Marathon bombing evidence This copy of The Sovereign, which calls itself the "newspaper of the resistance," was also found in Tamerlan Tsarnaev's apartment. Hide Caption 11 of 35 Photos: Boston Marathon bombing evidence Pictured here is a box of bullets found on a street after the shootout in Watertown. The brothers' fingerprints were on the box, prosecutors said. Hide Caption 12 of 35 Photos: Boston Marathon bombing evidence A pressure cooker was embedded in the side of a resident's Honda during the Watertown shootout. Hide Caption 13 of 35 Photos: Boston Marathon bombing evidence Photos of the Watertown shootout were entered into evidence. Neighbors came to their windows and then retreated. One grabbed his infant son and headed toward the back of his house with his wife. Another grabbed a camera and took photographs from an upstairs window. Hide Caption 14 of 35 Photos: Boston Marathon bombing evidence The Tsarnaevs had carjacked a Mercedes SUV in Watertown before the shootout. The vehicle was covered in bulletholes, and the rear window was shattered. Hide Caption 15 of 35 Photos: Boston Marathon bombing evidence This unexploded pipe bomb was found at the scene of the shootout between police and the Tsarnaev brothers in Watertown. Hide Caption 16 of 35 Photos: Boston Marathon bombing evidence Prosecutors said these boards were attached to the boat where police found Dzhokhar Tsarnaev hiding. A carved message reads, "Stop killing our innocent people and we will stop." Hide Caption 17 of 35 Photos: Boston Marathon bombing evidence Smashed phones and an ATM card owned by carjacking victim Dun Meng were in the yard where Dzhokhar Tsarnaev was found. Hide Caption 18 of 35 Photos: Boston Marathon bombing evidence Prosecutors say this surveillance image shows Tsarnaev visiting an ATM hours before a police chase and chaotic shootout in which more than 200 rounds were fired. Hide Caption 19 of 35 Photos: Boston Marathon bombing evidence Another view of Tsarnaev's visit to the ATM. Hide Caption 20 of 35 Photos: Boston Marathon bombing evidence Exhibits related to the shooting death of MIT Officer Sean Collier were introduced to the jury on Wednesday, March 11. This image from the crime scene appears to show a bloody gun. Hide Caption 21 of 35 Photos: Boston Marathon bombing evidence This burned tank top and yellow hoodie belonged to bombing survivor Jessica Kensky. Hide Caption 22 of 35 Photos: Boston Marathon bombing evidence Prosecutors say this Fox Racing logo was from one of the backpacks containing a bomb. Hide Caption 23 of 35 Photos: Boston Marathon bombing evidence Prosecutors say this still image from surveillance video shows Tsarnaev in the UMass Dartmouth gym the day after the bombings. Hide Caption 24 of 35 Photos: Boston Marathon bombing evidence Prosecutors showed the jury photos of what they say are Tsarnaev's writings inside the boat he was captured in. Hide Caption 25 of 35 Photos: Boston Marathon bombing evidence This image is from a surveillance camera outside the Forum restaurant in Boston's Copley Square just after the bombing. Hide Caption 26 of 35 Photos: Boston Marathon bombing evidence Prosecutors presented two Twitter accounts linked to Tsarnaev that, they said, showed targeting the marathon had been on his mind for at least a year. One account, @J_tsar, contained 1,100 tweets and was the more mainstream of the two. On the day of the 2012 Boston Marathon, a tweet from the account read, "They will spend their money & they will regret it & they will be defeated." Hide Caption 27 of 35 Photos: Boston Marathon bombing evidence Prosecutors said the second Twitter account is evidence that Tsarnaev led a double life. By day, he was a slacker college sophomore. By night, he was a wannabe jihadist, posting on the account @Al_firdausiA. In one tweet, he urged people to listen to radical cleric Anwar al-Awlaki's lectures. "You will gain an unbelievable amount of knowledge," he said in March 2013, just weeks before the bombings. Prosecutors also allege in an indictment that Tsarnaev downloaded al-Awlaki's writings, calling him a "well-known al Qaeda propagandist." Al-Awlaki had been killed in a U.S. drone strike in 2011. Hide Caption 28 of 35 Photos: Boston Marathon bombing evidence Hide Caption 29 of 35 Photos: Boston Marathon bombing evidence A Boston Marathon bombing victim is tended to in the street. Hide Caption 30 of 35 Photos: Boston Marathon bombing evidence Victims at the finish line just after the bombing. Hide Caption 31 of 35 Photos: Boston Marathon bombing evidence Eight-year-old Martin Richard, the youngest victim , can be seen standing on the rail in the front row. Hide Caption 32 of 35 Photos: Boston Marathon bombing evidence A closer view of 8-year-old Martin Richard in the crowd before the bombing. Hide Caption 33 of 35 Photos: Boston Marathon bombing evidence Boston police tend to a wounded child. CNN has chosen not to show the young victim's face. Hide Caption 34 of 35 Photos: Boston Marathon bombing evidence Mayhem along Boylston Street. Hide Caption 35 of 35

"Is his a life worth saving? Is there hope for him? Is there a chance for redemption?"

She reminded jurors of the testimony of Sister Helen Prejean, the Roman Catholic nun famous for counseling the condemned on death row. Prejean said she believed Tsarnaev was "genuinely sorry" for the pain and suffering he inflicted on his victims.

"That sounds like growth," Clarke told jurors Wednesday. "What unrepentant, unchanged, untouched young jihadi is going to meet with a Catholic nun. What unrepentant, hate-filled jihadi would even try to get her?"

Clarke is one of the nation's foremost experts on keeping clients off death row.

She has successfully fought for the lives of Ted Kaczynski, known as the Unabomber, and Jared Loughner , the gunman who killed a judge and wounded former U.S. Rep. Gabrielle Giffords in Arizona.

In the government's rebuttal, prosecutor Bill Weinreb repeatedly called Tsarnaev a terrorist and again sought to undermine the defense's portrayal of him acting at his brother's request. "Where is the evidence that he was under his brother's spell?

"The defendant deserves the death penalty -- not because he's inhuman but because he's inhumane."

He ended with: "If you sentence him to life in prison, you will be giving him the minimum punishment under law. Ask yourselves: Do these crimes deserve the minimum punishment?"