NEW HAVEN, Conn. (AP) — A Connecticut man convicted in a deadly home invasion is unlikely to commit serious violence if he spends his life in prison, a defense expert testified Tuesday.

A New Haven jury was hearing testimony it will use to decide whether Steven Hayes should he imprisoned for life or executed. He was convicted earlier this month of killing Jennifer Hawke-Petit and her daughters, 17-year-old Hayley and 11-year-old Michaela, at their Cheshire home in 2007.

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On Monday, a retired prison official testified Hayes threatened to kill a prison guard in March, saying he had nothing to lose.

Psychologist Mark Cunningham said Tuesday that Hayes would likely serve his sentence without seriously hurting an inmate or guard. He said the 47-year-old Hayes had already served 25 years in prison without committing serious violence and that prison violence is more likely with younger offenders.

Inmates killing correction officers are rare, with only one death per every 1 million prisoners, Cunningham testified.

Cunningham said his study of thousands of murder convicts concluded that they were not more likely to commit assaults in prison than inmates serving time for other crimes.

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He said jurors and psychiatrists who testify at trials often predict murderers will commit violence in prison, but studies contradict that belief.

“This is a body of research that is very counterintuitive,” Cunningham said.

Cunningham said his research in Missouri found that inmates serving life sentences were actually half as likely to be involved in assaults as parole-eligible inmates. He said prisoners serving life sentences may be motivated to avoid making their time tougher by losing privileges.

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