A family member discovered the bodies inside the Clinton home off Brooke Jane Drive, just after 7:30 a.m. Friday, after getting home from work.
Antonio Williams, 24, was arrested in connection with the murder of the three girls.
Police in Maryland said a man confessed to the fatal stabbings of his 6-year-old sister and his two young cousins while they were lying in bed.
Police are trying to determine what exactly happened inside of the home and say there is no threat to the community.More news: 3 children found dead inside home in Clinton
Prince George's County police identified the Newark girls as Ariana Decree, 9, and her younger sister Ajayah Decree, 6, of Palmer Street. Police said all three of them were pronounced dead at the scene.
On Saturday, Williams, 25, was charged with triple murder and according to charging documents, he confessed. "We have not determined who the person responsible is yet", she added.
Police were called just after 7:30 a.m. Friday morning to a scene that police spokeswoman Jennifer Donelan referred to as "one of the most hard scenes that our officers arrived on".
At a news conference Friday afternoon, Prince George's County Deputy Chief Sammy Patel said investigators were speaking with family members at police headquarters, but would not give any further details as to how they were related to the victims.More news: Statue of Pro-Slavery Supreme Court Justice Removed In Maryland
'This is one of the the most hard scenes that our officers arrived on, ' Donelan said, adding that the neighborhood where the children were found was quiet.
Relatives of the victims are being contacted and counseling has even been offered to officers who responded and found the bodies.
State's Attorney Angela Alsobrooks told NBC that Prince George's County had awoken to "yet another nightmare". "We all feel this loss", Velez said.More news: Carolina Panthers: Cam Newton again relegated to spectator