PENSACOLA, Fla. — Florida authorities were expecting more arrests — possibly as soon as today — in the killings last week of a Panhandle couple known for adopting children with autism, Down syndrome and other disabilities.

Authorities made three arrests over the weekend and a fourth Monday evening, but Escambia County Sheriff David Morgan said authorities believe "six to eight" people were directly involved in the crime. He said he hopes to make another arrest today.

Morgan said day laborer Gary Lamont Sumner was arrested on a murder charge in a nearby county Monday after he was pulled over in a traffic stop. The sheriff said investigators have placed Sumner at the scene of the killings of Byrd and Melanie Billings, though he wouldn't provide details.

The Billings took care to make their nine-bedroom house a safe place for their growing brood of children, wiring it with surveillance cameras in every room.

It was those cameras that captured images of the masked men who shot the wealthy couple to death in a break-in executed with chilling precision.

Morgan said the crime appeared to have "numerous motives," though robbery was the only one he would mention.

"Mr. Billings was well-to-do. He was an entrepreneur and he opened his home to the community. You are asking me to speculate on a motive. That could have been one reason," Morgan said, likening the killings to the 1959 slayings of a Kansas farm family. In that case, chronicled by Truman Capote in the book "In Cold Blood," the killers mistakenly believed the prosperous family kept a safe full of cash at home.