Authorities arrested Rodney Earl Sanders in connection with the murder of two nuns earlier this week.
Sanders has been charged with two counts of capital murder, and the Mississippi Bureau of Investigation says the crime has been resolved. But the motive in the case is still unclear.
CNN reports nothing was taken from inside the house, but the women's car was found abandoned about a mile away from their home.
The women worked as nurse practitioners at a clinic serving the poor.
"Margaret and I have worked together for many years. We just see patients and do what needs to be done," Merrill had said in a Sisters of Charity of Nazareth video.
Sanders is being held at an "undisclosed detention center" before his first court appearance.