Prosecution and defense lawyers wrapped up their cases yesterday in the trial of 10 young persons accused of murdering Catherine L. Fuller, and closing arguments are to begin today.

Prosecutors capped their case by calling several witnesses to rebut the alibi defense of Levy Rouse, who prosecutors say committed the most brutal attack on Fuller when she was killed Oct. 1, 1984.

Both sides then spent several hours arguing over how D.C. Superior Court Judge Robert M. Scott should instruct the jury on matters of law in the complicated case, which has included 57 witnesses and scores of exhibits during 21 days of testimony.

The final witness, D.C. police Detective Johnnie Green, told the jury that Rouse, 20, approached him two days after Fuller's death and mentioned a detail about Fuller's slaying that had not been publicized.

Green, who was assigned to the investigation immediately after Fuller's body was discovered in a Northeast alley, said he was told by Rouse that Rouse had heard that the "lady had jewelry taken from her" and that she had been beaten. "I didn't know anything about the jewelry or the beatings," Green said.

Green said that Rouse, who was in the courthouse that day as a witness in another case, had entered the U.S. attorney's office and asked Green a number of questions about the investigation of Fuller's death.

"That was a terrible thing that happened to [Fuller], the way she was beaten up," Green quoted Rouse as saying. Green said Rouse "just kept having this conversation . . . . He started telling me that 'the people who done it are going to get caught . . . . Somebody is going to tell . . . . They always tell.' "

When Green asked Rouse what he knew about Fuller's death, Rouse told the detective that a friend had seen the body and described it as "nude from the waist down" and mentioned the jewelry and beating, Green said. At that point, Green said, he notified one of the homicide detectives assigned to the case.

Rouse, who testified earlier that he was with his friend Christopher Taylor the afternoon Fuller was killed, has denied prosecution contentions that he was "unusually interested" in the investigation from the start.

Prosecutors contend that Rouse thrust a foot-long pole into Fuller's rectum after she was severely beaten and kicked during a robbery attempt over a coin purse and some jewelry.

Green and other police detectives testified yesterday that Taylor told them several times that he had witnessed Fuller's beating in the alley. Taylor has testified that he could not remember making any such statement to police and that on the day Fuller was killed he and Rouse spent the afternoon touring their Northeast neighborhood.

Rouse's former girlfriend Katrina M. Ward again testified yesterday that Rouse had told her that he had done "the worse thing to that lady in the alley." Under cross-examination, Ward, whose 4-month-old-daughter was fathered by Rouse, squirmed when asked what had prompted Rouse's remark. "He did something nasty in my kitchen," said Ward, explaining after repeated questioning that she had called Rouse a "nasty dog" after he exposed himself.

After Ward testified, defense lawyers once again criticized Rouse's defense and told the judge that Ward's testimony harmed all the defendants, most of whom Rouse has identified as friends. Steven Kiersh, the attorney for Steven Webb, unsuccessfully asked Judge Scott for a separate trial.