Vermont State Police investigators gave out few details at a news conference today, reiterating that they believe O'Hagan, 78, was "forcefully removed from her residence" but refusing to say how she died. Nor would they describe the condition of her body or say whether they have identified any suspects.
O'Hagan's body was found Sunday in the woods near Wheelock, Vermont, about 10 miles from her home in Sheffield, Maj. Edward Ledo, chief of the state police's criminal investigations bureau, said.
She was identified and an autopsy was carried out Monday, at which it was determined she had been murdered, he said.
"This turns the investigation into a new phase," Ledo said. "The fact that her body was found is a start, and it's a good turn."
Ledo was asked whether the fact that O'Hagan's killer or killers were still on the loose means that others were at risk. His answer: "At this point in time, someone is responsible for the murder of a 78-year-old woman, and they're still at large. People should take precautions, as they normally should."
None O'Hagan's five children were at the news conference, but Ledo read a statement from them.
"We are saddened by the news of our beloved mother, sister, grandmother and aunt," the statement said. "It is impossible to comprehend why someone would harm her.
"She was a wonderful person who was loved by many," it said. "She taught us the true meaning of family and faith, both of which became the foundation upon which we stood throughout her disappearance. She will be forever missed and never forgotten."
O'Hagan was last seen on Friday, Sept. 10, but was reported missing the following day, when she failed to show up for a rug hooking class she never missed.
The volunteers helped police and the FBI comb a 25-square-mile area around Sheffield, Vt., scuba divers even checked a nearby quarry, but there was still no sign of the missing grandmother.
"Anybody who has information relative to the case that can be helpful to please come forward," her son, Terry O'Hagan, said.
The mystery began Sept. 11, when a friend came to pick up O'Hagan for a rug hooking meeting. O'Hagan was nowhere to be found, but her car was still in the driveway.
Police said at the time that there was no reason to believe she had wondered off on her own.
Missing person signs were posted all over Sheffield, a quiet town of 700 people, while O'Hagan's children clung to memories of an active senior who cherished her family.
O'Hagan's family said they could not think of a motive for her abduction. In fact, they said, they were racking their brains trying to think of anyone who didn't like her.
"We've been looking and can't find anybody," said Maureen O'Hagan, her daughter.
But soon after beginning their investigation, police said they believed the woman, who enjoyed arts and crafts and was once the president of her town's historical society, had been abducted from her home.
"Based on the investigation and her known activities and the fact that she is very physically active and mentally sound, there is no reason to believe that she has wandered off on her own," said Vermont State Police Det. Sgt. Jason Letourneau in a statement to the press.
"I will not get into the details as to why we came to the conclusion that she left her residence against her will, but all indicators point in this direction," he said.
The FBI joined the search for O'Hagan, and authorities spent days combing fields, wooded areas and abandoned buildings searching for clues in the grandmother's disappearance.
O'Hagan's five children all traveled to Sheffield to help in the search.
Terry O'Hagan, 47, described his missing mother to ABC News as "not your typical 78-year-old retired woman."
"She is extremely active, she camps, kayaks, and volunteers at the library," he said. "We get exhausted reading the list of activities she's involved with."
Terry O'Hagan described his mother as extremely healthy for a woman of her age.
Missing Grandmother Pat O'Hagan Was Abducted from Her Vermont Home
O'Hagan moved with her late husband from Chelmsford, Mass., to Sheffield in the mid 1990s; her husband died a few years later in 2001.
Her children and friends said O'Hagan didn't have a boyfriend and had no financial windfall that would make her a likely target of abduction.
"She wasn't a rich woman," a friend, Francie Vos, told The Associated Press. "She was not stingy, but she had to watch every penny."
ABC News' Don Ennis contributed to this report.