Police: 6 to 8 believed involved in Florida couple's slaying

PENSACOLA, Florida (CNN) - Police believe six to eight people were involved in the shooting deaths of a Gulf Coast couple known for adopting special-needs children, authorities said Monday.

Those include three people already in custody in the deaths Thursday of Byrd and Melanie Billings, a crime Escambia County, Florida, Sheriff David Morgan called "a very well-planned and methodical operation."

"We are very hopeful that at least one more arrest and possibly two will occur today," as two persons of interest were being interviewed, Morgan told reporters. Two others have yet to be identified, he said.

Authorities have released two surveillance tapes taken from the front and rear of the Billingses' home. Each shows a vehicle pulling up to the property, and five people dressed in black and wearing masks entering the home from two different entrances - including through a utility door left unlocked, something Morgan said is not uncommon in the community. Authorities believe drivers remained behind in both of the cars.

Investigators believe one motive in the deaths was robbery, but "we believe there are other motives," Morgan said. He would not say what, if anything, was taken from the home.

–CNN's David Mattingly contributed to this report.