Released footage showed man in hoodie who may have taken family's Porsche found set ablaze Thursday in Prince George's County, Maryland

Police have ruled that the fire was intentional and consider it murder

Investigators think family held overnight by multiple suspects they knew

Fire was set at home and detectives found no sign of forced entry

Savvas and Amy Savopoulos found dead at their DC home on Thursday

A married couple, their young son and a housekeeper were 'bound and threatened' before being murdered in an arson attack by suspects who 'had knowledge of the family', according to police.

Savvas Savopoulos, 46, Amy Savopoulos, 47, and Philip, ten, were found dead along with housekeeper Veralicia Figueroa, 57, after the couple's $2million Northwest Washington DC home was set on fire on Thursday.

Investigators found no signs of forced entry and believe the suspects were able to gain access to the home on Wednesday and stayed overnight as they knew how the family 'lived their day-to-day lives'.

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Savvas, 46 and 47-year-old Amy Savopoulos were found dead after their Washington DC home was set albaze

Philip Savopoulos, ten, was also found dead along with housekeeper Veralicia Figueroa, 57, at the DC home

A friend told police that Savvas left a message saying Figueroa was staying overnight to help on Wednesday

Flames and smoke were seen billowing out of the upstairs window at the home before the bodies were found

It's believed the killers held the four captives 'bound and threatened' until Thursday afternoon, when Savvas, the CEO of American Iron Works, 'gave them what they were looking for', NBC reported.

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.

DC police and ATF agents continued to gather evidence at the Woodley Park home, which sits on Embassy Row near Joe Biden's house and the Clinton residence, on Monday.

Footage from the area police released Saturday night appeared to show a man dressed in a dark hoodie moving quickly behind a building.

Police believe the person of interest may have taken a 2008 Porsche 911 belonging to the family that was found set ablaze Thursday night in a church parking lot in Prince George's County, Maryland.

Footage from the area police released Saturday night appeared to show a man dressed in a dark hoodie

Police believe the person of interest might have operated a blue 2008 Porsche 911 belonging to the family

Police records show friends and relatives tried to reach the victims Thursday before they were found dead, according to the Washington Post.

According to the records, both Savopouloses sent text messages and voicemails 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 had told Gutierrez on Wednesday that his wife had plans to go out.

But in a voicemail that night, he said his wife 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 after hearing the message 'to see if she was OK, but she never answered.'

The couple's teenage daughters Abigail, 19, (left) and Katerina, 16, (right) were at boarding school at the time

Police documents show there were reports of unusual activity in the neighborhood before the arson

Gutierrez also knew Figueroa, the housekeeper who was found dead.

She told police that Savvas 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.

The house on Embassy Row is a few minutes away from Joe Biden's residence and the Naval Observatory

The Savopoulos family lived in the spacious $2million home on Embassy Row's Woodland Drive since 2002

The Savopoulos family has lived in the sprawling property on the 3200 block of Woodland Drive since 2002.

They also have a $240,000 two-bedroom condo in St Croix in the Virgin Islands.

Ten-year-old Philip was enrolled at $40,000-a-year St Albans School, a prestigious college-preparatory school on Embassy Row next to the Washington National Cathedral, which is visible from his family's home.

The family's two older daughters were not at home at the time of the fire, as they both attend elite boarding schools.