THE QUESTION that comes to mind about the brutal murder of Gloria Whipple is why at least one of the three men charged with killing her was on the street at all -- and not in jail -- when she was beaten and kicked on the Mall a month ago. You do not have to convict that man, Ray Anderson Leasure, in advance of his trial to know that he should never had been allowed to slip through the mechanism that is in place to keep potentially dangerous suspects off the streets.

The answer to why Mr. Leasure was not in jail on Sept. 17 begins in Courtroom 16 of Superior Court three months earlier. He -- and a second man, Charles P. Perkins, also charged with the Whipple murder -- appeared that day before Judge David Norman for arraignment on charges of rape and sodomy of an 18-year-old woman. While those charges alone might, or might not, have been found to justify holding the two in jail until after their trial, Mr. Leasure had something else going against him. He was already on probation after being convicted of assault and robbery .

Judge Norman began the proceeding that day by noting that the bail agency had suggested a preventive detention hearing if the government requested it. But the government didn't. Assistant U.S. Attorney Constance Belfiore asked instead for "a substantial surety bond." From the transcript, it appears that Judge Norman was stunned. "I don't understand that," he said. "He doesn't meet the standards [for preventive detention]?" A moment later, he told the prosecutor, "I'm not trying to put any pressure on you, but you can't use a money bond as an excuse for not having a preventive detention hearing."

A few minutes later, the two men were released after promising to return to court for their preliminary hearing and to stay away from the complaining witness.

While Assistant U.S. Attorney Belfiore has been unavailable to explain why a preventive detention hearing was not sought, colleagues in the U.s. Attorney's office explain that preventive detention is an option of last resort. The government doesn't like to go through the necessary hearing required to convince a judge that a defendant is a threat to the community. It fears that if preventive detention is not granted, the defendant will then be able to go after the people named by the government as witnesses. It also doesn't like the requirement that the case must be tried within 60 days if preventive detention is granted.

While the government's failure even to request such a hearing in this case was bad enough, its inability to follow up on the potential parole violation is even worse. In theory, when a person on probation is arrested for another crime, the judge who granted probation is notified and can send the suspect back to jail if the prosecution can show it is probable the defendant was involved in the new crime.

Judge Joseph Hannon, who granted Mr. Leasure probation on the earlier assault and larceny convictions, says he was never notified that Mr. Leasure had been re-arrested and charged with rape and sodomy. Alan M. Schuman, director of the Superior Court's social services division, said Mr. Leasure's probation officer did send the judge notification of the new arrest -- once orally and once in writing. Either way -- and it is possible the notifications were lost in the paper work and hectic pace of the courts -- nothing happened.

This picture of mix-ups, confusion and apparent gross errors of judgment is horrifying. Mr. Leasure might, or might not, have been held in preventive detention -- if the government had asked for it. He might, or might not, have had his probation revoked -- if a probation hearing had been requested. Judges are quite right in being stingy about putting defendants in jail before trial -- the presumption of innocence does cloak anyone charged with a crime. But provisions for pretrial detention and revocation of probation were not written into law frivolously. They were put there to make it possible for the government to keep potentially dangerous persons off the streets.

Revocation of probation should not be automatic when a person is charged with a new crime. But a revocation hearing should be, especially when the new crime is as serious and violent as that with which Mr. Leasure was charged. And the government should not shy away from preventive detention hearings in cases like this one when defendants already know the identity of the principal witness against them -- the victim.

These suggestions are born of frustration and sadness over the inequities of a system of justice that seems to us to have utterly failed. Mrs. Whipple's daughter, a criminal justice student at Marquette, put it best when she said: "This really makes me want to get into it [criminal justice]. I don't understand this."