A woman returning from work Thursday discovered a young boy decapitated and her two daughters slashed to death in their apartment in a working-class neighborhood in the northwestern section of the city, police said.

The bodies of the three children, a 10-year-old and two 9-year-olds, were found in the first-floor apartment when the mother came home about 5:40 p.m., police said.

"No parent should have to see their children like this," said Antonio Williams, chief of the 3,300-member Baltimore police department's detective division. "It was brutal."

Police said last night that they were questioning a man who had been named by the mother. They found him a few blocks away. They said the man, whose name they withheld, may once have lived in the apartment. But they were unable to say whether he was related to the woman, who was described as speaking little English.

Police said they did not know the relationship between the boy and the mother of the two girls.

After discovering the children, the mother rushed from the apartment shouting for help in Spanish. When she was unable to explain to a neighbor what had happened, she took the neighbor to the apartment and showed her the carnage.

"I've seen my share of murders," Deputy Police Chief Kenneth Blackwell said. "And I've not seen anything as gruesome as this. Anyone who's had a child or knows a child would be affected by what I saw. It's one of the saddest things I've ever seen. It's something I'll remember till I draw my last breath."

Mayor Martin O'Malley, visiting the crime scene, called the incident "a brutal, tragic, unfathomable, sad murder of three young children."

The two-bedroom apartment in the 7000 block of Park Heights Avenue was well-kept, clean and did not appear to have been ransacked, a police source said.

Walking into the apartment, officers found the boy's body lying chest down in a bedroom to the right of the front door, according to the source.

The two girls were found facedown in a bedroom across the hall, the source said. The victims appeared to have been beaten with a baseball bat or another object before being slashed with a large knife, the source said.

In the yard, police recovered what they believe is the murder weapon, apparently tossed out a back window of the apartment, according to the source.

The knife had only a small amount of blood on it, said the source, who described the weapon as having about a 10-inch blade.

Police sources said two mothers and their families, all immigrants, had been living in the apartment for several months. The spouse of one of the mothers also lived in the apartment, sources said.

Blackwell said detectives were studying entryways to the home to see whether force was used. Spanish-speaking officers were helping to interview several men who were brought to the homicide office last night, police said.

Police officials said that the neighborhood is quiet and that those who lived there had no reason to fear for their safety.

"We see this as an isolated incident," he said. "It's very uncharacteristic of this neighborhood to suffer through this type of tragedy."

Police said the children returned home from school shortly after 3:30 p.m. Neighbors said they saw the three chasing cicadas in a courtyard within a couple of hours of when their bodies were discovered.

Lena Johnson arrived at work across the street from the apartment building and found that police officers and crime lab technicians and vehicles were occupying the entire block.

"It's pretty intense," said Johnson, a night technician and medical assistant at Senior Hospitality, an assisted-living building.

"This is a first. I've never heard of anyone getting shot up here or beaten to death," Johnson said. "It's just a sad, sad situation."

Emmanuel Hyde, who has lived in the neighborhood since 1993, lamented that "the country is getting scary."

"We don't know what kind of society our grandchildren are going to live in," Hyde said.

Staff writers Clarence Williams in Washington and Phuong Ly in Baltimore contributed to this report.

L. Johnson, who refused to give her first name, stands at the door where the mother pounded after finding the bodies.Baltimore Detective Will Rogers, gesturing, talks with other investigators outside the apartment in Baltimore where the three were killed.