Baltimore police detectives scrambled yesterday to unravel the circumstances behind the gruesome slaying of three young children in their apartment last week but had not determined a motive for the attack that they say was committed by relatives.

Charging documents released yesterday revealed new details about the crime and potential evidence recovered by authorities, including a shirt and towel with suspected blood seized from the suspects' suburban home.

Despite an intense investigation into one of the city's most brutal killings in recent years, police officials said yesterday that they were no closer to understanding why the two relatives, Mexican immigrants, would savagely behead one young boy and slash the throats of two other children.

"Detectives are working feverishly to figure it out," Deputy Police Commissioner Kenneth Blackwell said yesterday.

The suspects, Adan Espinoza Canela, 17, and Policarpio Espinoza, 22, were being held without bail on first-degree murder charges. They are scheduled to appear at a bail review hearing Tuesday.

The children slain late Thursday afternoon in their first-floor northwest Baltimore apartment have been identified as Lucero Quezada, 8; her brother, Ricardo Espinoza, 9; and their male cousin, Alexis Espejo, 10. The children were members of an extended family of Mexican immigrants. The children and their immediate family members were in the country illegally, officials said.

A relative of the suspects said yesterday that he could not imagine the two men committing such a crime.

"Nobody can believe it," said Alberto Juarez, the brother-in-law of Adan Espinoza's father. "We don't think they are capable of that crime."

Police said they were led to the two men by a person who approached a detective as he canvassed a crowd gathered at the crime scene Thursday night.

The person described having witnessed two men "acting in a suspicious manner just outside the victims' apartment window" a few days before the attack, according to the charging documents.

That person pointed out the two men who were chatting with the victims' family members at the crime scene, the documents show.

The witness gave a detailed description of the suspects and told authorities that the men had been "peeping" into the apartment windows, police sources have said.

Detectives took the two men -- identified as Adan Espinoza and Policarpio Espinoza -- into custody. Policarpio Espinoza was the uncle of two of the victims, and Adan Espinoza was their cousin. They were both more distant relatives, through marriage, of the third victim.

The men speak little English, and Adan Espinoza refused to talk with authorities, according to charging documents.

Policarpio Espinoza told detectives through a Spanish-speaking interpreter, the documents show, that he and Adan Espinoza were at the apartment Thursday between 4:20 and 5 p.m. -- just after the children arrived home from school and minutes before the bodies were discovered by another relative.

Policarpio Espinoza told the investigators that he drove Adan Espinoza to the apartment. The 17-year-old knocked at the door, and one of the children answered it, allowing Adan Espinoza to enter the home, the documents show. Policarpio Espinoza told detectives that he remained outside in the car, a Pontiac Grand Am with Virginia tags, and later saw Adan Espinoza emerge from the apartment through a back window.

Adan Espinoza "directed" Policarpio Espinoza to a nearby school parking lot, where he got into the car, according to the court papers. Adan Espinoza was not wearing a shirt when he returned to the car and told Policarpio Espinoza that he had been playing with the children, the documents show.

It is not clear where the pair drove after getting into the car.

Police recovered a butcher knife with about a 10-inch blade just outside the apartment's back window. It had what police believe was blood on it, according to the documents.

Police later searched the suspects' one-story house in suburban Baltimore County, the documents show, and recovered a shirt and towel that had "suspected blood on them."

The items and others seized are being analyzed by evidence technicians, police said.

Yesterday afternoon, police detectives continued to question the victims' relatives, including the father of two of the children, about potential motives for the slayings.

Staff writer Nurith C. Aizenman and staff researcher Bobbye Pratt contributed to this report.

Adan Espinoza Canela, 17, left, and Policarpio Espinoza, 22, are being held without bail in Baltimore on three counts of first-degree murder. They are scheduled to appear at a bail review hearing Tuesday.