It's a decision, the judge told the jury, that is “grave and awesome.”
The state rested its case in the penalty after just one witness on Monday morning and Hayes' defense attorney is urging a jury to keep an open mind as it considers the death penalty.
Hayes was convicted on Oct. 5 of the 2007 murders of Jennifer Hawke-Petit and her daughters Hayley, 17, and Michaela, 11.
Six of the 16 charges for which Hayes was convicted carry the possibility of the death penalty, including the murder of multiple victims, the murder of a person under the age of 16, and the murder of a victim of sexual assault.
The same jurors who found Hayes guilty of the crimes now must weigh both aggravating and mitigating factors in their decision of whether to sentence Hayes to life in prison or sentence him to death.
The state’s one and only witness on Monday went through Hayes’ arrest record, which includes burglary charges in 1981 and 1993 and burglary convictions in 1996 and 2003.
Patrick Culligan said on Monday that his client had a powerful drug addiction that controlled his life and the arguments moved to whether Hayes intended to kill the Petit women.
Hayes' attorneys expect to call six to eight witnesses on Monday to present the case of who Hayes was before the Cheshire slayings.
Part of the case will include reading from a diary the other suspect, Joshua Komisarkevsky kept.
Prosecutor Michael Dearington told jurors of the victims suffered cruel deaths.
On Sunday, the eve of the start of the penalty phase, some Cheshire residents expressed their thoughts on what they think should happen. Some said they hope the jury does the right thing.
"I, for one, will be disgraced and disgusted if the death penalty is not given on this disgrace of a human," Paul Paniccia said.
"I think death should be a right decision for both of them," said Vilan Kosover, who said he thinks the jury would sentence Hayes to death.
Because Hayes was convicted on all six capital counts, some legal experts believe members of the jury have already made up their minds about his fate.
He said that a decision might come quick.
The penalty phase began this morning in New Haven Superior Court.
Follow updates from court here.