DURANT, Miss. — A memorial Mass was to be held today for two 68-year-old nuns who were killed in their Mississippi home, even as authorities continue to investigate the stabbings. A man from about 15 miles away has confessed without giving a reason, according to the sheriff.

The Mass will be at the Cathedral of St. Peter the Apostle in Jackson, about an hour’s drive from Durant, the town of 2,500 where Sisters Margaret Held and Paula Merrill lived until last week.

They both worked at a health clinic for the poor in nearby Lexington, where they also led Bible study at a church. And more than 300 people came Sunday to St. Thomas Church to say farewell, even though more than half had to watch the vigil for the deceased on a monitor outside.

About 145 people filled the church to capacity, and there was an overflow crowd outside, where 160 folding chairs were set up and still people had to stand to watch on a monitor as Bishop Joseph Kopacz of the Jackson Diocese led the service.

The church’s priest, the Rev. Gregory Plata, spoke about how far-reaching the nuns’ work was.

The final hymn, described as Sister Margaret Held’s favorite, was “How Can I Keep from Singing?”

Afterward, nuns from the dead women’s orders, people from other faiths, and members of the community embraced the women’s families.

The killing shocked people in the small communities where the women committed their lives to helping the poor.

Rodney Earl Sanders, 46, of Kosciusko, Miss., has been arrested and charged in the stabbings. The county sheriff said Sanders confessed to the killings although many people are struggling to comprehend why anyone would want to take the two women’s lives.

Their bodies were found after they failed to show up for work Thursday at the clinic.

Authorities have said Sanders was developed as a person of interest early in the investigation.