The mother and father of 16 children were shot to death in their home while some of the family were asleep upstairs.

The couple had an extensive surveillance system in their Florida home that recorded three seemingly experienced criminals swiftly slip into the house before driving off in a red van, police said. Byrd and Melanie Billings were found shot dead in their home on Thursday evening.

Investigators were led to a red, 15-passenger vehicle on Saturday morning that they believe was used as a getaway car by the three men, believed to be in their late teens or older, Escambia County Sheriff David Morgan said. Authorities were questioning two people linked to the van, but no arrests have been made.

"I will share this with you - I think we were surprised by the rapidity of the crime," Morgan said after authorities reviewed the surveillance tapes. "It suggests experience to me." However, officials still don't know why the family were targeted.

The couple were well-known 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, among which 12 are adopted. Eight of them, aged 8 to 14, were in the house when their parents were killed. They are now staying with relatives.

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

They said, in a 2005 story in the Pensacola News Journal, they wanted to share their wealth with children in need, but didn't imagine their family would grow so large. "It just happened," Melanie told the newspaper. "I just wanted to give them a better life."

[via DailyMail]