The latest in a series of shocking murders that have shaken this city -- the brutal killing of three children Thursday -- was not the work of vengeful drug lords or an act of random violence, investigators said Friday.

Instead, an uncle and cousin in a family of Mexican immigrants who operate a fleet of taco trucks on downtown streets allegedly used a 10-inch butcher knife and a club to kill three members of their family, an 8-year-old girl, her 9-year-old brother and their 10-year-old cousin.

There was no explanation from police or surviving family members for the killings.

"It just doesn't make sense," Kenneth Blackwell, the deputy chief of police, said last night. "Everybody is speculating, but nobody can really tie clear motives to this thing. It just doesn't make sense."

The killings were the latest of several horrific slayings that have underscored that Baltimore has one of the nation's highest violent crime and homicide rates. Three years ago, three homeless men were stomped to death on city streets by a pair of teenagers and another young man. Two years ago, seven members of one family died when their home was firebombed after they complained to police that drug dealers were in control of their east Baltimore neighborhood. And two weeks ago, twin infants were found beaten to death, allegedly by their parents, in the trash-strewn basement where they lived.

A subdued Mayor Martin O'Malley (D) told reporters Friday that "a brutal, heinous murder happened in our city last night." And neighbors stopped at the apartment building, leaving a makeshift memorial of flowers and balloons at the front door.

"I can't put into words how I feel about this," said Margo Lambert, who lives a few blocks away with her 11-year-old daughter. "When a child is killed like this, it's like it's a child of all of us. And the way they were killed -- I just can't imagine how someone could be so heartless. You'd have to have no soul to kill a child in this manner."

The two suspects were identified by police as Adan Espinoza Canela, 17, and Policarpio Espinoza, 22. Each was charged with three counts of first-degree murder.

"We're confident we have the main suspects in the case," said Antonio Williams, chief of the Baltimore police department's detective division.

Police said the suspects entered an apartment in the 7000 block of Park Heights Avenue shortly after the children returned home from school Thursday, attacking them with a bludgeon and with a knife that was recovered from the back yard Thursday night.

The dead children were identified as Lucero Quezada, 8; her brother, Ricardo Espinoza, 9, and their male cousin, Alexis Espejo, 10. (Police initially described the victims as a boy and two girls.)

Relatives and police said the victims and the suspects were members of an extended family that arrived in recent years from the town of Tenenezpan in Veracruz state, Mexico.

A family member said one suspect, Policarpio Espinoza, was the uncle of Lucero Quezada and Ricardo Espinoza. The other suspect, Adan Espinoza, was their cousin. Both suspects were more distant relatives of Alexis Espejo through marriage.

The immigration status of the two suspects was unclear Friday, but family members and another source confirmed that all of the victims and their parents were in the country illegally.

The parents of the dead siblings, Mimi Quezada and Ricardo Espinoza, arrived in the country about seven years ago and relocated to Baltimore later, starting a family taco truck business. Quezada's niece, Maria Andrea Espejo, came to Baltimore with her son, Alexis, early this year and moved into the apartment on Park Heights Avenue, family members said.

The suspects were living with another family member, Victor Espinoza, whose house in a quiet residential section of northwestern Baltimore County was searched by police Friday. It was unclear whether the suspects were employed in the taco truck business.

The following account of the slayings was drawn from interviews with police, neighbors and family members.

Shortly after 3 p.m. Thursday, the three children boarded their school bus outside Cross Country Elementary School, a boxy brick building less than two miles from their home.

A few minutes later, they were dropped off in front of the home of a woman who, until a few months ago, had been their babysitter. But after the arrival of Alexis from Mexico this year, Mimi Quezada had decided that the three children were old enough to fend for themselves in the hours after school.

So, the children and their neighborhood friends amused themselves chasing cicadas as they made their way about a half-block to the three-story, red-brick building where they shared a first-floor apartment with their parents.

The children were the face that the family presented to their neighbors because the adults spoke little English, which proved a barrier to conversation with neighbors.

The cicada chase -- the bugs were out in raucous force that afternoon -- continued in the courtyard at the center of the apartment building for a while before the children disappeared inside.

"They played out in the square every day after school with the other neighborhood children," said Heather Hopkins, 25, a neighbor.

An hour or so later, Antionette MacDonald said, she was looking for a playmate for her niece and wondered whether Lucero would emerge from the apartment.

"I asked my daughter, 'Where's Lucero?' " MacDonald said. " 'Why didn't Lucero come out?' The next thing you know, I'm hearing her mother screaming."

The adults had returned home after a day of operating their food truck on the streets of Baltimore about 5:40 p.m. They unlocked the apartment door and discovered that the safety chain had been engaged from inside, so they called out for the children to open it.

It was silent inside, so Ricardo Espinoza walked around the building and climbed through an open bedroom window. The women heard his screams from the hallway, and when he released the door chain, their voices joined his own.

Mimi Quezada rushed from the building in search of help.

"The mother came outside screaming that something happened to her kids," said Tamiko MacDonald, 39, a neighbor, "and everyone came running out of their apartments to help."

Unable to communicate the problem effectively, Quezada rushed one neighbor into the bloody apartment, where a child lay decapitated in one bedroom and two others were bludgeoned and slashed to death in another.

A crowd quickly gathered outside the building as police swarmed around it, and Irvin Bradley, a veteran Baltimore detective, worked his way through it, asking whether anyone had seen anything suspicious.

One person, whose name was withheld by police, described two men who had been behaving oddly outside the building this week, a police source said.

"The witness said the men were peeping in windows and scoping out the place," the police source said.

Bradley gave out his business card, which has his cell phone number, as he made his way through the crowd.

Later that night, as he continued to canvass the crime scene, Bradley's cell phone rang. It was the witness, who said the two "suspicious" men were standing in the crowd that lingered outside the building.

"The description was accurate down to the color of one of the guy's hair," said the police source.

Two men, Policarpio Espinoza and Adan Espinoza, were taken into custody minutes later in front of the building, police said.

Early Friday, police said, one of the men gave a statement implicating both in the crime. Police would not say which man made the statement.

They said no motive was offered.

Yvonne Bankston and other Baltimore residents hold a prayer vigil near the building where the children died.Adan Espinoza Canela, 17, left, and Policarpio Espinoza, 22, were charged with three counts each of first-degree murder.Baltimore Police Academy cadets search for evidence in a field near the apartment where the children were killed.Rodolfo Juarez, 12, is a second cousin of the slain children. With him is his uncle Ignacio Salinas, 27, a distant relative of the victims and the suspects.