Michael Lorenzo Tubman pleaded guilty yesterday to killing 4-year-old Monica Wheeler in a drug-fueled rage while the girl was in his care in September. But the Southeast Washington man will not be charged in the death of Monica's brother, Andre, three years ago. Although police have said in court that they suspect Tubman killed Andre, too, prosecutors have agreed not to pursue that case as part of a plea bargain in Monica's death.

Tubman, 32, an acquaintance of the children's mother, told a D.C. Superior Court judge yesterday that he was high on drugs when he beat Monica to death Sept. 23 in his Southeast Washington apartment. Her slaying led authorities to review the circumstances of 2-year-old Andre Wheeler's death on Oct. 9, 1994 -- and to reclassify the official manner of his death from accident to homicide.

Now it's a homicide that may go forever unpunished.

"I think there's something we all can learn from this -- whether it's my office, the medical examiner's office or police," Assistant U.S. Attorney June M. Jeffries said. "I'd like to view this as a learning experience."

The case is another testament to problems that have plagued the D.C. medical examiner's office in recent years. The office has drawn criticism for not showing sufficient expertise in the handling of child deaths. Its practices also have come under scrutiny in the deaths of six women in the Petworth area of Northwest Washington. After police began investigating the possibility of a serial killer at work in that neighborhood, the office changed its manner-of-death rulings from undetermined to homicide in two of the cases.

In Monica's case, Tubman told the judge yesterday, "at the time of the situation, I was under the influence of drugs." According to Jeffries, Tubman has told authorities that he was under the influence of phencyclidine, or PCP, a hallucinogen that can induce extremely violent behavior.

"I didn't know how hard I was hitting her because of the drugs," Tubman said in court. "I just tried to pop her so she would lay down and I could go to the bathroom and finish smoking my drugs."

In Andre's case, although an autopsy detected five bruises on his head, the medical examiner's office initially listed the manner of death as undetermined. Then the office changed its ruling to an "accidental drowning," accepting Tubman's account that he inadvertently had left the boy alone in a bathtub.

Tubman told D.C. police homicide investigators that he had been giving Andre a bath but was interrupted by a telephone call. He said he then became engrossed in a Washington Redskins football game on television and forgot about the child. He said he checked on Andre 40 minutes later and found him dead.

"Because it looked like an accident and {Tubman} appeared remorseful, when the medical examiner gave her ruling, that's where it stayed," Jeffries said. "You did not have the level of investigation that we would have liked."

It was only after Monica's death that the medical examiner's office again changed its ruling in Andre's case, reclassifying his death as a homicide. Jeffries said that Deputy Medical Examiner Marie Lydie Y. Pierre-Louis -- who had made the earlier rulings in Andre's case -- changed the manner of his death to homicide based strictly on Monica's death, without making plans to exhume Andre's body.

When homicide detectives arrested Tubman after Monica's slaying, they had warrants charging him with two counts of second-degree murder -- one in Monica's case, the other in Andre's. Jeffries said she decided at that time to go forward only in Monica's case, believing that further investigation might yield new evidence in Andre's.

She said she held out hope of eventually filing charges in Andre's death, and in September, she cited Andre's case in arguing that Tubman should be jailed without bond in Monica's slaying. In agreeing to order that, Judge Truman A. Morrison III said there was reason to suspect Tubman of killing Andre.

However, Jeffries said yesterday that she had concluded it would be nearly impossible to overcome a jury's doubts and convict Tubman in Andre's case.

"If we were to go to trial, the {initial} ruling that his death was accidental would certainly have come up as an issue," she said. "That would never go away. . . . This would be a case that would present fodder for expert witnesses."

Jeffries said the plea bargain was in the best interests of the victims' family because it saved them an "emotionally exhausting trial." The crimes to which Tubman pleaded guilty -- manslaughter and cruelty to a child -- are punishable by up to 40 years in prison. He is scheduled to be sentenced March 10. Police said there were no witnesses to Andre's death. There were no witnesses to Monica's slaying, either. But from the start there was little question about how the girl had died, police said. She had numerous bruises on the head and body, her back was broken, and she had bled heavily from internal injuries.

At 6 a.m. Sept. 23, Tubman summoned police to his apartment in the 3600 block of 22nd Street SE, saying he could not wake up Monica. He told police that he had been watching Monica and three of her siblings -- ages 1, 2 and 6 -- and that Monica had appeared all right when she went to bed the previous night.

A much different story emerged in court yesterday.

Assistant U.S. Attorney Amy J. Conway, who handled the case with Jeffries, said Tubman beat Monica so severely she could barely move or breathe. After beating Monica, Tubman left his apartment to "cool off," Conway said. When he returned and found that her condition had worsened, he attempted to cover up the crime by putting Monica in a bathtub filled with water and calling 911, Conway said.

Tubman then gave his account to Judge Mary Ellen Abrecht -- his story of a drug-induced rage.

"Do you admit beating her?" Abrecht asked him.

"Yes," Tubman said. Staff writer Sari Horwitz contributed to this report. CAPTION: The slaying of Monica Wheeler, above, led to a review of the circumstances of the death of her brother in 1994. CAPTION: At left, Michael Lorenzo Tubman enters guilty plea before Superior Court Judge Mary Ellen Abrecht in the death of Monica Wheeler, 4, pictured above, while prosecutors and the defense attorney look on.