Sixteen people were shot in Baltimore City over the Labor Day weekend, six of them fatally, including a young mother killed Sunday evening by a stray bullet as she tidied up after a holiday gathering of family and friends. All the victims of the weekend's violence deserve swift justice, but none more that Larelle Amos, a 22-year-old former honors student at Kenwood High who leaves behind a 1-year-old son. Now is the time for incoming city police commissioner Anthony Batts to show the leadership Baltimore expects of the city's top cop. His first assignment should be to make sure Larelle Amos' killer is brought to justice.

Police are still investigating the sudden upsurge in violence that occurred over the weekend. A department spokesman said the number of shootings over such a short time is extremely unusual and that investigators are still unsure whether any of the incidents are linked. Some of them appear to have been drug- or gang-related, and at least one involved a robbery. Investigators speculate that whoever killed Ms. Amos may have been targeting someone else among the party of more than 100 guests at the house and that she was caught in the crossfire. The police are urging anyone with knowledge of the incident to come forward.

One of the most vexing questions raised by this latest spate of shootings is whether they represent something more than an unfortunate coincidence, a statistical blip in an otherwise steady downward trend in violent crime, or whether they signal some new development in the criminal world that requires a different response from police. Under former commissioner Frederick H. Bealefeld III, the department adopted a nuanced crime-fighting strategy that focused on the small group of violent offenders who commit most of the serious crime and on seizing illegal guns.

That targeted effort paid off by bringing city homicides to the lowest level in decades. But last weekend's resurgence of shootings is a reminder that the city's progress under Mr. Bealefeld remains fragile. Officials should take it as a warning that the downward trajectory in violent crime seen in recent years is not irreversible.

On Tuesday, Acting Police Commissioner Anthony Barksdale, who is leading the department until Mr. Batts arrives later this month, called a war-room meeting of his top commanders and urged them to proceed as quickly as possible in the investigation. The initial response has included beefed up patrols by both uniformed and plainclothes officers in the areas where the shootings occurred and an intensified intelligence effort to identify the nexus of relationships connecting the victims and possible suspects. Forensic and ballistics personnel are working overtime to identify the weapons used in the attacks from shell casings and bullet fragments found at the crime scenes.

All of this is taking place at an awkward time for the city. Mayor Stephanie Rawlings-Blake is in Charlotte, N.C., for the Democratic National Convention, and Mr. Batts, who isn't scheduled to start work until Sept. 27, is still on the West Coast. Both receive daily briefings as the investigation unfolds, but their lack of a visible presence in the city after such a traumatic episode sends the wrong message. The police are asking residents to make sacrifices by stepping in to help them solve these vicious crimes; the mayor and new police commissioner should be standing alongside them. Perhaps this would be a good time for them both to consider altering their schedules.

Mr. Batts, in particular, has strongly endorsed Mr. Bealefeld's policy of targeting the relatively small number of criminals who commit most of the city's crime, and he's also an enthusiastic supporter of policing strategies aimed at enlisting the community's help in catching the bad guys. This is an opportunity for him to make that appeal in person at a time when it really matters. While he's at it, he should demand justice for all the victims of last weekend's shootings and add a pledge that whoever was responsible for the death of Ms. Amos will be found and brought to justice.