MILLINOCKET – Kevin Ingersoll didn’t think much of it, at first. The town police officer was off-duty in Miller’s Department Store buying a pair of pants on Thursday when he saw a woman who looked out of place.

“I didn’t recognize her as a local individual, so I went up to her and I said hi,” Ingersoll said Friday. “She just looked at me and walked off. She didn’t say anything.”

Ingersoll immediately recalled the brief encounter when he went to work Friday and saw a missing-person bulletin out of Massachusetts. He believes, and the store owner confirmed, that the missing person is the woman he saw at Miller’s, he said.

The woman is Michelle Harrison, 53, of Newburyport, Mass., who disappeared March 16 in a case that baffles Lt. Robert Gagnon of the Newburyport Police Department as much because of what it isn’t as what it is.

As far as investigators can determine, Harrison is not a crime victim. Nor is she suffering from any physical or mental ailment or any kind of personal problem or sudden trauma that would explain her absence, Gagnon said.

Harrison is a special education teacher at a private institution. She seldom misses work, has three adult children and, by all accounts, enjoys a healthy family life, usually telephoning her children if she doesn’t hear from them first, Gagnon said. Harrison has no ties to the Katahdin region that anyone, including her grief-stricken family, is aware of.

She is simply missing.

“I have been here 28 years, and this is probably the first case like this that I have run into,” Gagnon said Friday. “I’m not saying it never happens, but it’s not one that you see every day.”

Harrison apparently left her home on March 16 carrying a house key and a car key, Gagnon said. She left some money behind. EZ Pass hits traced her white 2005 Subaru Legacy station wagon on Thursday along Interstate 95 north to the Hampton, N.H., tolls, where she was last tagged heading south at 10:44 p.m. She was reported missing the next day.

Police have no reported sightings of the car since, nor have they detected any credit card or cellular telephone activity, Gagnon said.

About the only thing police know, Ingersoll said, is that she likes water and the outdoors, which are abundant in the Katahdin area.

Anyone who might have seen her car, which carries Massachusetts license plate 7644PA, is asked to contact Newburyport police at (978) 462-4411 or Millinocket police at 723-9731.

When Ingersoll saw her, he said, she was wearing a blue and gray coat and appeared normal.

Gagnon hoped Ingersoll’s sighting was genuine.

“Her family is distraught. The uncertainty of the whole thing is eating away at them terribly,” he said. “They would like to get some more concrete information as to her whereabouts and well-being.”