WHITE CREEK -- In March 2010, as he neared the end of parole for a grand larceny conviction, Matthew A. Slocum stole his mother's 2003 Ford Mustang and drove it to his uncle's home in New Hampshire.
Slocum and the vehicle were found in New Hampshire days later. The car was returned to New York, and Slocum was arrested. But his mother, Lisa Harrington, refused to have him prosecuted, officials said.
Matthew Slocum wound up back in state prison to serve the remainder of his 1 1/3- to 4-year state prison sentence, which amounted to two months.
He was released on June 30, 2010, and he was not on parole because he had served 4 years between prison and parole.
Thirteen months later, on the morning of July 13, 2011, police say Slocum stole the very same Mustang and again drove it to his uncle's home in southwestern New Hampshire.
This time, he took the car after he allegedly shot his mother, her husband, Daniel A. Harrington, and her husband's son, Josh O'Brien, to death before dawn Wednesday in their Turnpike Road home in Eagle Bridge. He allegedly set the home on fire afterward.
Alerted by local police to the possibility he might flee to New Hampshire again, New Hampshire State Police were watching the uncle's home in Gilsum, N.H., when the black Mustang appeared and the driver tried to hide the car under a blue tarp outside the home, police said.
A standoff of more than four hours ensued before Slocum, 23, was taken into custody.
Police said both he and his girlfriend, Loretta Colegrove, cooperated with police after they were found. She was in the home at the time of the killings but has not been charged, according to police.
The police investigation continued Friday, with Washington County sheriff's investigators awaiting final word on autopsies of the three victims, as well as formal identification of the bodies, Undersheriff Matthew Mabb said.
Police were also working to recover guns that were stolen from the home and may have been used in the shootings, Mabb said. Police were told the weapons were abandoned on a roadside in Massachusetts on Wednesday, he said.
Police have not determined what they believe prompted Slocum to kill the three, the undersheriff said. While investigators have said he "cooperated," he has not provided details about what transpired before the early morning deaths.
"He hasn't revealed anything that would indicate a motive," Mabb said.
Police are looking into information from relatives that the Harringtons had been asking Slocum to move out of their home, Mabb said.
"There has been some talk about that," he said.
Authorities said Slocum has had years of run-ins with the law.
In 2006, as he dealt with cascading legal problems that were pushing him to state prison, Slocum was reviewed by Washington County Drug Court officials for possible participation in the county's drug court program for felons. There were indications he was abusing alcohol and marijuana during a months-long crime spree, officials said.
The coordinator who reviewed his background made it clear he was not ready for the program in a report that cited Slocum's "extreme anger" issues and emotional problems, an official who reviewed the report said. The person requested anonymity because the report was not public information.
Washington County District Attorney Kevin Kortright said his office was not in favor of allowing Slocum into the drug court program because of his criminal history, and prosecutors sought a state prison sentence instead.
Slocum wound up sentenced to 1 1/3 to 4 years in state prison for grand larceny in connection with two home burglaries and for his involvement in the 2005 theft of a safe from a Cambridge grocery. He was paroled in 2009 but violated parole twice and was returned to state prison both times.
Cambridge-Greenwich Police Chief George Bell said Slocum's mother came to his home the night last year that her car was taken, asking for his help.
Bell said it was common for her to intervene on her son's behalf during his run-ins with the law - beyond what police typically see with parents whose children repeatedly get arrested.
"Any time he got in trouble, she came to us about it," he said. "She always defended him. I think she was intimidated by him."
Relatives of the family spoke outside court Thursday night about how much Harrington did for her son.
"She did everything for that kid," Harrington's brother, Raymond Coon, said, adding that Slocum didn't deserve to live for what he was accused of doing.
Slocum's extensive criminal history included a sexual misconduct arrest for allegedly having sex with an underage girl in 2005, as well as involvement in the 2005-2006 burglary and larceny cases.
There is also a pending harassment charge in Greenwich Town Court against him for allegedly making a threat toward another person, though details of that charge were not available Friday.
He has been charged with three counts of second-degree murder and one count of first-degree arson and is being held in Washington County Jail without bail pending a preliminary hearing on Tuesday in White Creek Town Court.
He could face 100-years-to-life in state prison if convicted of all four charges.