The 24-page form to sentence Boston bomber

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When the state decides whether or not to put someone to death, it approaches the matter in a methodical way. But as jurors are discovering, the decision is about emotion as much as logic.

Nearly everyone agrees about the nature of the crimes Dzhokhar Tsarnaev committed. They were horrific.

Martin Richard, eight, was killed by a bomb Tsarnaev placed at the Boston Marathon finish line. So were Krystle Campbell, 29, a restaurant manager, and Lingzi Lu, 23, a graduate student at Boston University.

The bombs maimed 16 people and injured many more.

Tsarnaev and his brother, Tamerlan, later shot and killed Sean Collier, 27, a police officer.

But now the jurors are facing an emotionally fraught issue, with two outcomes. Tsarnaev will either be put on death row or in prison for the rest of his life.

On Thursday morning the jurors, a group made up of five men and seven women, walked into the courtroom, dressed casually in short-sleeved blouses and shirts.

To help the jurors along, officials have put together guidelines.

Some are straightforward. The jurors must agree, for example, Mr Tsarnaev was over the age of 18 when he committed the crimes (he was 19).

Yet some are hard, such as the fourth statement jurors must weigh - "Dzhokhar Tsarnaev demonstrated a lack of remorse".

They will also be asked to evaluate whether his "friends still care for him".

These guidelines are rooted in the US Constitution - the eighth amendment bans "cruel and unusual punishment". The Supreme Court has decided that means special care must be taken before someone is sentenced to death.

The process is designed so only a certain kind of murderer, the most heinous, is subjected to the most severe punishment.

But it imposes structure on a process that may seem overwhelming.

"The Supreme Court really wants it to be clear which steps led the jury to a death sentence," said Stephen Vladeck, a law professor at American University Washington College of Law.

For that reason the jurors consider aggravating factors, such as a defendant's lack of remorse, as well as mitigating factors, such as a troubled family background, when they decide whether or not to impose the death penalty.

If the jurors cannot agree on a death sentence, the judge will sentence him to life in prison without parole.

It gives the process a scientific air, ensuring that a rigorous process is in place. Yet a decision about whether someone lives or dies is more than a bureaucratic one.

In this case, Judge George O'Toole Jr told the jurors they should not provide him with "a numerical count" of where they stand - how many jurors voted for each aggravating or mitigating factor.

In a similar way, defence lawyer Judy Clarke told jurors it wasn't a "numbers game". She held up the guidelines on Wednesday during her closing argument - a stack of documents held together with a heavy, black paperclip.

This is not a situation, she says, in which "the longest list wins".

And while it may be enshrined in US law, it is also an individual decision. One juror, dissenting from the others, can ensure Tsarnaev will live.

"Whether a sentence of death is justified is your own individual decision," Ms Clarke told the jurors.

Mr Vladeck agreed. He believes the decision is about a legal matter, though, and is not a moral or ethical one.

"It's just their job to answer a series of very specific legal questions," he said

Not everyone agrees.

"We try to treat what's going on as a heavily structured legal process, but there's no denying that there's a critical moral aspect," said Daniel Richman, a professor at Columbia Law School.

On Thursday afternoon the jurors returned to the courtroom.

The judge told them not to speak about the case and to return in the morning to resume deliberations.

At some point - perhaps soon - the foreman will collect the forms and give a summary of their views to the judge.

In this way the fate of Tsarnaev will be decided.

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