A puncture wound to the brain and a ruptured spleen killed the 2-year-old. But D.C. detectives said it was the code carved into the soft skin of the toddler's back that identified his attacker.

The combination at first was a mystery to investigators, who had a young suspect in mind. They showed photos to a guidance counselor at the youth's D.C. middle school. He drew a blank, then turned to a youngster who said he knew what it meant.

KDY4 stands for 4th and Kennedy Street Crew, the boy said. It also matches the markings on a stuffed animal found in the bedroom of a 12-year-old boy now charged with first-degree murder.

The 12-year-old had spent three weeks before the killing at the home in the 700 block of Kentucky Avenue SE, according to testimony in D.C. Superior Court. On July 10, police and prosecutors believe, he killed Julio Guy Thomas in a most brutal way.

The Washington Post generally does not, as a matter of policy, identify juvenile offenders. A reporter attended a Tuesday court hearing, otherwise closed to the public, with the understanding that the youth's identity would not be revealed.

At the hearing, prosecutors argued that the case against the boy is strong. Defense attorney Carl MacPherson countered that police work was shoddy, important witnesses and suspects remained uninterviewed and the homicide charge was unjustified.

"This is the worst-investigated case I've ever seen," MacPherson said after he cross-examined Detective Don Sauls for more than two hours. The lawyer described parts of the investigation as "absurd" and "absolutely ridiculous."

D.C. Hearing Commissioner Fern Flanagan found enough evidence to uphold the murder charge, ordering the seventh-grader to a shelter home to await trial. She described Sauls's testimony as credible and the KDY4 evidence as significant.

"I think a lot of this is circumstantial," Flanagan said, "but I think it's strong circumstantial . . . even the inscription on the child's back."

Charging a 12-year-old with murder is "unusual but not unheard of," said David Rosenthal, chief of the D.C. corporation counsel's juvenile division. From 1996 to 1998, the office prosecuted 27 youths younger than 18 for homicide, including five children ages 10 to 14. During the same period, the U.S. attorney's office filed murder charges against 65 youths who were 16 or 17 years old. The number of defendants has declined from 28 in 1996 to 23 in 1997 to 14 in 1998 to six so far this year, said Channing D. Phillips, a spokesman for the U.S. attorney's office.

The standard of evidence is the same whether the defendant is charged as an adult or a juvenile, but there are no grand juries or petit juries in juvenile court, and the stakes are quite different. A suspect convicted of first-degree murder in adult court must spend 30 years to life in prison. In juvenile court, where judges are granted wide latitude, there are no minimum sentences. Whatever the crime, the youth must be freed before age 21.

Julio Thomas was at home with his father, a cousin and several brothers and sisters the day he died. His family ate dinner together after 9 p.m. July 9. Afterward, his father and one of the 2-year-old's brothers carried Julio and his 1-year-old sister upstairs to bed.

Julio's father, Raymond L. Minor, told police that he heard no screams between 9 p.m. and 6 a.m., when one of Julio's brothers brought the dead boy downstairs. Minor said that the brother had reported the previous night that Julio was vomiting but that he did not go upstairs to check on his son.

Minor told police that he went to Safeway for a half-hour with a cousin after 2 a.m. but otherwise was at home, Sauls testified. At D.C. General Hospital on July 10, the detective said, Minor was "hysterical. He started crying."

Sauls, the lead detective, said he rejected all other suspects and settled quickly on the 12-year-old as the probable killer. He said Minor was never a suspect.

In court, MacPherson countered that Minor's statements to police were self-serving: "Raymond Minor has so many reasons to lie. He has no credibility at all. Everything Raymond Minor says doesn't make any sense."

One child said Julio's 3-year-old sister had pushed the toddler down the stairs, but a D.C. morgue doctor said any such fall was not the cause of death. Sauls said under cross-examination that the doctor was not told of the pushing allegation before conducting the autopsy.

Julio was badly bruised. His neck had marks that suggested a throttling. His ribs and one arm were broken. Signs indicated someone had tried to pull one of the boy's arms from its socket. His brain had been punctured by a sharp object.

"He had carvings on his back," Sauls said. On Julio's lower back, were the letters KD. Across his back was a Y. In the upper left was a 4. A second morgue doctor said the cuts seemed the work of a child. In the 12-year-old's room, Sauls said, police found a stuffed animal. On one side was the numeral 1. On the other, KDY4.