Woburn, Mass. ? Thomas Mortimer IV called his new boss and told him he was too sick to come to work. He called his 4-year-old son’s school to say the boy would be absent. When his wife’s sister called, he told her it would be a while before she could return the call.

And, prosecutors say, he wrote two identical letters found in his Boston-area home that read: “I did these horrible things. What I’ve done was extremely selfish and cowardly. I murdered my family.”

Mortimer, 43, was captured Thursday by police in northwestern Massachusetts hours after he was charged with four counts of first-degree murder in the deaths of his wife, two young children and mother-in-law.

The day before, authorities were summoned to the Mortimer family home in Winchester by a relative who could not reach them.

Officers found the bloodied body of Mortimer’s wife, Laura Stone Mortimer, 41, and their son, Thomas Mortimer V, known as Finn, in the front hallway.

Not far away, they discovered the body of Mortimer’s mother-in-law, Ellen Stone, under an oriental rug. And upstairs, at the end of a trail of blood, was the body of Mortimer’s daughter, Charlotte, 2, in her crib.

All appeared to have been killed by a combination of blunt trauma and sharp objects, prosecutors said.

District Attorney Gerry Leone said there were signs Mortimer had attempted suicide before he fled the home in Winchester, an upper middle-class suburb north of Boston.

Leone said the slayings followed a fight and “ongoing marital discord.”

The discovery of the bodies led to a search for Mortimer, with police issuing alerts about his sport utility vehicle on electronic signs across the state. A man who had seen news reports about the search and recognized the SUV called police — after helping Mortimer jump-start his stalled vehicle in Montague.

Mortimer was spotted by police in Bernardston, about 100 miles from Boston, and captured after a brief pursuit.

Leone said the exact time of the slayings was still being determined but appeared to be sometime between late Monday and early Tuesday.

Mortimer called in sick to work on Tuesday and called his son’s school to say he would not be in.

Leone said his wife’s sister, Debra Stone, tried to call her Tuesday, but instead Thomas Mortimer answered her cell phone — which was highly unusual.

Thomas Mortimer told Stone, “It’s going to be a while before she can get back to you,” Leone said.

Mortimer was scheduled to be arraigned today in Woburn District Court for the killings, which the prosecutor described as “brutal and unspeakable.”

Mortimer had recently landed a job at M&R Consultants Corp., a Burlington technology consulting firm, after several months of unemployment, said Anil Shah, the company’s president. Mortimer was a hard worker who had been making progress at his job since getting hired about a month and a half ago, Shah said.

“He was very professional, very nice guy … always very positive,” he said. “Somehow my heart doesn’t believe he could be involved in anything that he’s been charged with.”