District of Columbia police have released surveillance video of a "person of interest" in the slaying of a family and their housekeeper in a multimillion-dollar northwest Washington home that was set on fire.

Footage that police released Saturday night appears to show a person dressed in dark clothing moving quickly behind a building. Investigators are also looking for information about a 2008 blue Porsche belonging to the family that was found set ablaze Thursday night in Prince George's County, Maryland.

Police have identified two of the victims found dead as 46-year-old Savvas Savopoulos and his 47-year-old wife Amy Savopoulos. Investigators believe the other two victims are the couple's 10-year-old son, Philip, and a housekeeper, Veralicia Figueroa, 57, of Silver Spring, Maryland.

D.C. Police Chief Cathy Lanier said all four were homicide victims, and at least three of them suffered stab wounds or blunt-force injuries. The injuries occurred before the family's home was set on fire Thursday, Lanier said.

The Washington Post (http://wapo.st/1A72dze ) reports police records show friends and relatives tried to reach the victims Thursday before they were found dead. According to the records, both Savopouloses sent text messages and voice mails to a housekeeper telling her not to come to their home to clean on Thursday, which had been her normal routine.

Nelitza Gutierrez, the housekeeper who received the messages, told the Post the series of messages left her thinking something was amiss with her employers. Gutierrez had worked for the family for 20 years.

Savvas Savopoulos had told Gutierrez on Wednesday that his wife had plans to go out. But in a voice mail that night, he said Amy Savopoulos had been sick in bed.

"It was something very suspicious because I felt his voice was really tense," Gutierrez said in Spanish. "And it was different than what he had said to me before."

Gutierrez said she called Amy Savopoulos after hearing the message "to see if she was OK, but she never answered."

Gutierrez also knew Figueroa, the housekeeper who was found dead. Gutierrez told police that Savvas Savopoulos left a message saying Figueroa was staying overnight to help, saying that his wife was sick and his son was home with an injury.

Gutierrez said she had never known Figueroa to stay overnight. "Never, never did she stay over," Gutierrez said.

Police documents also show there were reports of unusual activity in the neighborhood. Neighbors reported seeing a man banging on the door of one home. There was an aggressive vacuum cleaner salesman at another house and reports of a prowler.

A witness also reported seeing what could have been Savopoulos' blue Porsche speeding down the street the day before the deaths were discovered.

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Information from: The Washington Post, http://www.washingtonpost.com