St. Louis County Prosecutor Bob McCulloch announces the grand jury's decision not to indict Ferguson police officer Darren Wilson in the August 9 shooting death on Michael Brown at the Buzz Westfall Justice Center in Clayton, Missouri, November 24, 2014. A Missouri police officer has not been charged for the fatal August shooting of an unarmed black teenager, an incident that set off weeks of sometimes violent protests around the St. Louis area, a county prosecutor said on Monday. (Pool/Reuters)

AFTER WEEKS of anticipation, protesters in Ferguson, Mo., heard on Monday night the news they had feared: A St. Louis County grand jury declined to indict Ferguson police Officer Darren Wilson in the killing of Michael Brown, an unarmed African American teenager shot dead by Mr. Wilson this summer.

The burning and looting of local businesses that followed cannot be condoned or excused. But the frustrations of Ferguson residents — most of whom have behaved lawfully since protests began over the summer — are more than understandable. A life had been lost needlessly. Now the process of holding Mr. Wilson to account had gone easy on the officer. And though the grand jury declined to indict Mr. Wilson, the evidence it heard — even Mr. Wilson’s own account — makes clear that wiser policing on that August day would have saved a life.

St. Louis prosecutors used kid gloves when questioning Mr. Wilson before the grand jury. They practically coached the officer to describe the area where the shooting occurred as hostile to police. They went out of their way to note that Mr. Wilson cooperated with investigators. A more challenging process would have pressed Mr. Wilson on critical details, such as why he got out of his cruiser in pursuit of Mr. Brown after an initial confrontation with the teenager, rather than waiting for backup. That would have required self-restraint, but it also might have prevented Mr. Brown’s death. The record brings home how justice would have been better served had Missouri authorities named a special prosecutor to pursue the case.

Despite all of this, President Obama was right Monday night when he called on people to respect the grand jury’s decision. The process wasn’t perfect, but it was legally legitimate, the result of 12 citizens poring over reams of conflicting evidence. Given the contradictory nature of much of the record, the grand jurors faced a tough call, and a trial might very well have resulted in an acquittal.

One immediate lesson from Ferguson is that the police should be collecting more evidence all of the time — by means of body cameras worn by officers. The grand jurors had access to plenty of eyewitness accounts, but those varied dramatically. Cameras, too, have drawbacks. They can’t show what’s happening off-screen, which can lead to false impressions. Police can manipulate camera angles or even disable the devices. Yet experience suggests that, among other things, increased use by police of body cameras tends to reduce the number of confrontations.

It’s hard to know how this incident would have played out with cameras recording the encounter. Perhaps the grand jury would have had a clearer picture of who attacked whom first, whether Mr. Brown charged at Mr. Wilson before he was shot and whether Mr. Brown insisted that he wasn’t armed. It’s also possible that the confrontation would have occurred differently, or not at all.