The judge in Zacarias Moussaoui's death penalty trial admonished the jury Friday to avoid dictionaries after learning a juror looked up the meaning of "aggravating."

How aggravating and mitigating factors balance out in the jurors' minds is key to their deliberations, which resumed after a daylong break called because one juror was sick.

Moussaoui can only be executed for his part in the Sept. 11, 2001, attacks if the jury believes unanimously that his crimes involved at least one of three main aggravating factors alleged by the government. If so, the jury must consider mitigating factors offered by the defense before reaching that decision.

The jury of nine men and three women is deciding whether Moussaoui should be executed or given life in prison.

Deliberations halted briefly Friday after the court learned that a juror had turned to a dictionary — which U.S. District Judge Leonie Brinkema had refused to supply the jury earlier in the week when asked. Brinkema decided in a closed hearing that the juror's misstep wasn't significant enough to stall deliberations further, but told the jury not to look up words again.

She has also cautioned the jurors, who go home each day, not to do online research.

She said aggravating "essentially means to make something worse" and pointed to jury instructions that define aggravating factors as "factors or circumstances that tend to support the death penalty."

Moussaoui, after the hearing and out of the jury's presence, declared loudly, "Moussaoui aggravating curse on America."

Earlier in the week, Brinkema denied the jury's request for a dictionary, saying that to supply them would be like placing extraneous evidence in jury room.

Although the verdict will come down to one central question — whether Moussaoui lives or dies — the jury is having to consider dozens of questions on a 42-page verdict form — each a piece of the puzzle about who this man is, what he did and what penalty he deserves.

In this case, prosecutors alleged three main aggravating factors for each of the three counts against Moussaoui. At least one must be proved beyond a reasonable doubt. They were that he committed his crimes in an especially heinous, cruel or depraved manner; that he committed his crimes knowing others besides the intended victims might die; and that he used substantial planning or premeditation.

Then they added seven more aggravating factors, such as a lack of remorse, for the jury to consider separately. These extra factors, known as non-statutory, are optional elements meant to add weight to the federal case.

For any such condition to stick, the jury must accept it unanimously. If none of the three main aggravating factors is proved, the case is over and Moussaoui goes to prison for life. But if any of the conditions are accepted by the jury, then 23 mitigating circumstances raised by the defense must be weighed, one by one.

Among them: Do jurors agree Moussaoui will not be a substantial risk to guards if imprisoned for life? Do they agree he was an ineffectual Al Qaeda operative? Do they think he really believes he will achieve the afterlife rewards of a martyr if he is executed?

Altogether there are 33 such questions, to be weighed up to three times for each separate count.

Unlike the prosecution, the defense does not have to prove its factors beyond a reasonable doubt or achieve unanimity on the jury. If any of the jurors thinks a mitigating factor is more likely true than not true, it becomes a factor for the jury to consider.

There is no formula for assigning weight to various factors, even if jurors do decide they exist. Jurors can decide one aggravating factor outweighs all mitigating factors, or the other way around.

In the end, it still comes down to life or death and what the jurors think. The questions tell them some of what they have to think about.