FORT HOOD, Texas (CNN) -- Family members of victims of the Fort Hood massacre were prepared to testify Monday about their grief, as the sentencing phase for Maj. Nidal Hasan's court-martial moved quickly toward a dramatic conclusion.

A military jury by Tuesday could begin considering whether Hasan will get capital punishment for the November 2009 shootings on this sprawling Army base.

The Army Medical Corps officer was convicted Friday on all 13 counts of murder and 32 counts of attempted murder in connection with the shooting rampage at a Fort Hood deployment processing center. The incident occurred about a month before Hasan was to deploy to Afghanistan.

The sentencing phase began Monday with Hasan again insisting he represent himself as his own attorney. The Army judge, Col. Tara Osborn, called it "dangerous, disadvantageous."

"You are staking your life on the decisions you make," she told Hasan. "It is unwise for you to represent yourself, but that is your choice."

The panel of 13 senior officers is expected to hear two or three days of testimony in open court during the sentencing phase.

Military officials say prosecutors could present more than 16 witnesses, including a liaison or family member for each victim killed in the attack. They will describe the impact the shootings had on their lives, part of the "aggravating" evidence the prosecution will use to try to demonstrate why Hasan deserves lethal injection.

During the nearly three-week trial phase, military prosecutors called 89 witnesses and submitted more than 700 pieces of evidence.

Unclear is whether Hasan himself will now present testimony or speak on his own behalf. He has so far refused to put on a defense in court.

The American-born psychiatrist of Palestinian descent has the opportunity to offer "mitigating" evidence that could persuade the panel to spare his life.

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