A young boy and girl were found dead, and their two siblings were found severely injured, inside a Germantown, Md., townhome Friday morning, police say.
Police are questioning the children's 28-year-old mother, who tried to run from the home when officers responded to the scene, law enforcement officers told News4's Pat Collins.
They're also questioning another woman, 21, who was found in the home with superficial injuries. She is not believed to be a relative but is believed to have lived in the home.
None of the victims or the people being questioned has been identified, but detectives said the deceased children were a 1-year-old boy and a 2-year-old girl and the injured children are a 5-year-old girl and an 8-year-old boy.
Police said the deaths are being investigated as a double murder.
The scene in the townhome in the 1900 block of Cherry Bend Drive in Germantown -- which State's Attorney John McCarthy called "horrifying" in a press conference Friday afternoon -- was discovered after neighbors saw a commotion outside.
"...[O]ne of the neighbors here saw what they thought appeared to be blood near a car," said Montgomery County police Capt. Jim Daly.
A neighbor called 911 saying he saw a blue car with its door open and the knife on the sidewalk outside the house. Police who responded to the scene about 9:30 a.m. saw a blue car with its door open. The keys were in the ignition and there was blood in the car.
Police also found a knife on the sidewalk outside. Police believe the red-handled knife may be one of the weapons used in the attack.
Officers had to force their way into the home and found the victims inside in a "very bloody" crime scene. The children were found in the bedrooms and may have been asleep at the time of the attack.
Witnesses described seeing the officers bring out the victims. "I did see a police officer holding a child ... it was a little kid," said one neighbor, who did not want to be identified.
The injured children were transported to Children's Hospital in northwest Washington, where they are being treated.
Police were called to the home Thursday night by a neighbor to check on the welfare of a child left unattended in the blue car, Pat Collins reported. By the time the police responded, the child had been taken inside. The case was reported to Child Protective Services.
Neighbors later said they heard loud noises coming from the townhouse, but they did not call police.
Police have not identified the victims, but neighbors said that at least one attended Germantown Elementary School. That school, and nearby Clemente Middle School, sent a note home to parents. That note did not confirm that the students attended the school but acknowledged the tragedy.
"The incident did not occur on our property and at no time was there any danger to our students or staff in the school," the note read.
Stay with News4 and NBCWashington for more on this developing story.