Investigators believe the D.C. family found dead in their burning home last week may have known their killers, who were able to bypass a complex security system that witnesses say was always on.

Savopoulos, his wife, Amy, their son, Phillip, and their housekeeper, Veralicia Figueroa, were all found dead Thursday when firefighters responded to a fire at their $4.5 million northwest D.C. home.

The nature of the family’s security system, which was apparently always on and chiming—even when everyone was home—has led cops to believe there was a relationship between the killers and the family. Investigators tell NBC Washington there was no sign of a forced entry and that they believe the killers “had easy access.”

Police also believe the family was held captive overnight, NBC Washington reports.

Investigators believe it’s likely that the killers gained access to the home Wednesday and kept the victims bound and threatened through Thursday afternoon, when Savvas Savopoulos gave them what they were looking for, sources said.

There’s already some public evidence to support that theory: Nelitza Gutierrez, a second housekeeper referred to as “Nelly,” says the family behaved oddly in the days before the murders.

For example, she claims she received a bizarre phone call from Savvas Wednesday night explaining that Figueora—who was spending the night—had been unable to charge her cell phone. He then allegedly requested Nelly “tell that to anyone who might be worried about [Figueora].”

Nelly also tells CNN she received a text from Amy just a few hours before the fire that read, “I am making sure you do not come today.”

Image via NBC Washington. Contact the author at gabrielle@gawker.com