His family was worried about Jacob Gallant’s whereabouts, but nothing he said led them to suspect the violent turn the Westport man’s life would take over the weekend.

Mr. Gallant, 41, of 457 Adamsville Road (not far from the Little Compton line), was arrested by Warwick, RI, police Sunday afternoon. He is accused of using a large knife that afternoon to stab an 18-year-old employee of a Rite-Aid store in that city in what police believe was a random act of violence.

The young woman was reported to be in serious but stable condition Monday.

Westport Police became involved at 10 a.m. Saturday when a family member — an aunt — called to say that the family was worried because they hadn’t spoken to Mr. Gallant since Friday at around 7 a.m., Westport detective Jeff Majewski said.

The aunt said that he was “agitated and crabby” in that conversation and also said it was uncharacteristic of him not to return to his home that evening.

As is standard procedure, Westport Police then entered Mr. Gallant’s name into the FBI’s National Crime Information Center database.

Other than that agitated call, Det. Majewski said the family reported nothing especially unusual although it was learned that Mr. Gallant may have been concerned about possibly having to move out of the family home. He had no police record.

Police said that on Thursday he visited Fall River Hyundai as a customer and struck up a “perfectly normal” conversation with another customer, a young woman. She later said that he had mentioned that he might have move out of the house where he lived and relocate to Florida.

That evening he met his aunt and two cousins for dinner at the Roasted Pig restaurant in New Bedford and, by their accounts, acted as usual.

Det. Majewski said police learned that Mr. Gallant, whom they believe is unmarried, lived in the house owned by his grandmother before she died fairly recently. There may have been bank-related issues that led him to think he would soon have to move elswhere.

Police also learned that Mr. Gallant never showed up at work Friday (Det. Majewski could not confirm the nature or place of that work). Nor had he been in touch with the only friend mentioned, a person from Little Compton.

Maybe, a family member said at one point, he disappeared because he needed some time to clear his head, the detective said.

“It remains unknown where he spent the time" from Friday morning until Sunday afternoon, Det. Majewski said.

He was driving a grey Hyundai, license plate 7434SJ, and anyone who may have seen him or that car during the period is urged to call Westport Police.

“You never know what is going to make someone snap in today’s world,” Det. Majewski said.

He also said that, while it might not have made a difference in this instance, the “old TV myth that you have to wait 24 hours to report someone missing” is not the case. The moment there is concern, “don’t hesitate to call.”