Florida law enforcement officials said Saturday that the people who killed a couple in their Panhandle home last week as their children slept appeared experienced.

Escambia County Sheriff David Morgan said in a news conference that the department is questioning two persons of interest but they are not in custody. He said tips from the public led to the discovery of a red van Saturday morning that was likely the same one used in the crime and that helped authorities find the people they are questioning.

Byrd and Melanie Billings of Beulah, a rural area west of Pensacola near the Alabama border, were found shot dead in their home Thursday evening. The couple, known for their large family of adopted children, had an extensive surveillance system in the house and Morgan said authorities have reviewed the tapes repeatedly.

"I will share this with you -- I think we were surprised by the rapidity of the crime," Morgan said.

"It suggests experience to me," the sheriff added, "the rapidity of this crime -- in and out" of the couple's home.

He said officials "have yet to determine a reason for, specifically why the Billings were targeted."

The sheriff said he would not comment on whether anything was taken from the family's home. He said the three suspects being sought in the crime are in their "late teens on up" in age. The department had released a grainy photo of a red, 15-passenger van on Friday and said they believed it carried three men involved in the killings.

The couple was well known locally for adopting children with developmental disabilities. They owned several local businesses, including a finance company and a used car dealership.

The Billings had 16 children, 12 of them adopted. Eight of the children, ages 8 to 14, were in the home when the couple was killed. Investigators interviewed the children, who are now staying with other family members.

They couple married 18 years ago and each had two children from previous marriages. They eventually started adopting children with developmental disabilities and other problems.

In a 2005 story in the Pensacola News Journal, the couple said they wanted to share their wealth with children in need, but didn't imagine their family would grow so large.

"It just happened," she told the newspaper. "I just wanted to give them a better life."