New Haven , Connecticut ( CNN ) -- A man convicted of killing a mother and her two daughters during a brutal 2007 Connecticut home invasion can be `` quite likable , '' but has struggled with drug addiction for years , a defense attorney told jurors Monday . The same jurors who convicted Steven Hayes of capital murder and other charges convened Monday for Hayes ' penalty phase . They will decide whether he should be sentenced to death for the slayings of Jennifer Hawke-Petit and her daughters , 17-year-old Hayley Petit and 11-year-old Michaela Petit . Attorney Patrick Culligan told jurors in his opening statement they will hear testimony from `` people who know Steve Hayes , whose lives have crossed paths with Steven Hayes ... to try to give you some insight , some understanding of who Steven Hayes was prior to the crimes of July 23 , 2007 . '' Some of the testimony , he warned , will not be flattering to Hayes , but he said that despite his long history of criminal convictions and drug abuse , Hayes could be `` quite likable . '' `` There is no presumption at this point that the death penalty is the appropriate punishment , '' Culligan said . `` ... You must keep an open mind . '' Culligan said testimony would also focus on Hayes ' behavior in prison in the past , noting that he has been incarcerated for `` most of his adult life '' because of his addiction . `` At the conclusion [ of testimony ] , you 'll come to know much more of the 'who ' about Steven Hayes , '' Culligan told jurors . `` ... Hopefully , you 'll also have a fuller understanding of his role in these crimes ... these most horrible and tragic crimes . '' Hayes , 47 , was convicted earlier this month of 16 of the 17 charges against him , including nine counts of murder and capital murder and four counts of kidnapping . Jurors acquitted him of an arson charge . During the penalty phase , jurors will determine whether the mitigating evidence the defense is expected to present outweighs the aggravating factors in favor of the death penalty . Jurors are allowed to consider evidence they heard during the guilt phase of the trial . They can also consider new testimony or evidence that attorneys introduce during the sentencing phase -- which might include the defendant 's long history of prior convictions and anything that casts Hayes in a positive light . Hayes himself could testify . `` All of the evidence presented in the guilt phase may be considered in this phase ... and the state is relying on that evidence , '' prosecutor Michael Dearington told jurors in his opening statement . The only new testimony presented in the penalty phase by the prosecution concerned Hayes ' prior convictions -- two in 1981 and others in 1993 , 1996 and 2003 , all for third-degree burglary . The prosecution rested just before the court took a lunch break Monday . The killings took place in the New Haven suburb of Cheshire , a brutal attack that shocked the well-to-do community and drew nationwide attention . The home of Dr. William Petit was invaded in the middle of the night by Hayes and another man , Joshua Komisarjevsky , prosecutors say . Komisarjevsky will be tried separately . Connecticut State Police Detective Anthony Buglione , who interviewed Hayes after the crime , has testified that the duo beat Petit bloody and left him in the basement . According to testimony , the two men then went upstairs and found Hawke-Petit and Michaela asleep in the master bedroom . After tying Hawke-Petit to her bed , they led the girl to her room , tied her to her bed and put a pillowcase over her head , Hayes told Buglione . They then found Hayley Petit in her room and did the same , he said . After finding evidence of a bank account containing $ 20,000 to $ 30,000 , they decided to have the mother go to the bank in the morning and withdraw money from her account , Buglione testified . Hayes is accused of taking Hawke-Petit to the bank while Komisarjevsky allegedly stayed behind . When Hayes and Hawke-Petit returned with the money , the two men allegedly set the home on fire and fled . Inside the home , authorities said , Hawke-Petit , 48 , was found raped and strangled . Her two daughters , one of whom had been sexually assaulted , died of smoke inhalation . Petit , the sole survivor , escaped to a neighbor 's home . William Petit has said he will not offer a victim impact statement during Hayes ' penalty phase , saying in a statement he `` regretfully '' decided against doing so because Connecticut 's law on victim impact statements is unclear and could provide convicts with grounds to appeal their sentences . Culligan noted in his remarks to jurors Monday that `` There was another person involved in this crime : Joshua Komisarjevsky . '' He said jurors will hear about Komisarjevsky in the suspect 's own words , much of it from his writings to author Brian McDonald . Judge Jon Blue has suggested the penalty proceeding could last as long as four weeks , though the relatively quick pace of the guilt phase of Hayes ' trial has led some to speculate the penalty phase could also be quick . Hayes ' attorneys had sought to introduce testimony regarding the comparative cost of life imprisonment versus execution , but Blue barred the subject .
NEW : Defense attorney asks witnesses to keep an open mind . NEW : Prosecution offers testimony on Steven Hayes ' prior convictions . NEW : Defense says Hayes has struggled with drug addiction for years . He could face the death penalty for killing a mother and child .