(CNN) -- From the outside, Carol Coronado embraced motherhood. She played with her three girls -- ran after them, kissed them, smiled with them, a neighbor recalled. Her children seemingly had no shortage of joy, as evidenced by their own abundant laughter.
"She (said) she loved being a mother," Ashley Madrid said of Coronado, her neighbor.
But the inside -- at least inside her Southern California home on Tuesday -- was a different story. According to the Los Angeles County Sheriff's Department, Coronado is believed to have killed her children. The oldest was 3 years old, the youngest all of 2 months.
Sheriff's deputies arrived at a home in unincorporated Torrance early Tuesday evening to find "family members who told (them) that a mother had killed her children." Inside, they found three juveniles dead and their mother "adjacent" to them, the sheriff's department said.
Authorities told CNN affiliate KTLA the young girls were lying in a pool of blood. Their naked 30-year-old mother was holding a knife, investigators told the same station.
Coronado eventually emerged from the house, wearing little more than a blanket. Madrid told Nancy Grace of CNN's sister network HLN that Coronado looked blankly at the ground.
"I could see the blood smears all over her face and arms and legs," Madrid recalled. "And she was just stone-faced."
The mother was brought to a local hospital, then to the department's Carson Station to be booked on murder charges, said the sheriff's department. As of Wednesday evening, online records didn't indicate that Coronado was officially an inmate in the county, and it wasn't known whether she had a lawyer.
So exactly what happened? And why?
There's been no official word about a motive, nor has the sequence of events been spelled out.
Madrid had known Coronado since the latter moved into the neighborhood four to five years ago.
In that time, Madrid and Coronado would talk at the grocery store or across the fence about their children. Never did she hear any arguments or see any signs of trouble.
"Never," the neighbor said Wednesday. "Completely opposite of what happened yesterday."
The girls' father was across the street working on a car when it happened, Madrid said.
"I can't imagine how he feels, you know," Robert Marino, a family friend, told CNN affiliate KCAL. "It's just not right."
CNN's Sonya Hamasaki and Ed Payne contributed to this report