SHORTLY AFTER the Metrobus he was driving barreled through a red light downtown and plowed into a taxi occupied by a visiting business executive and his family, Ronald W. Taylor told a police officer at the scene what happened. “I didn’t see the light,” Mr. Taylor said, according to court papers. “I didn’t see the taxi.”

The accident near the Federal Reserve, in September 2008, killed Bartlett M. Tabor, the businessman, and left his wife as well as the taxi driver with injuries. Witnesses reported that the bus shot through the red light, an account Mr. Taylor’s statement seemed to confirm. The black box aboard the bus established that Mr. Taylor was speeding, according to prosecutors.

Despite a multimillion-dollar civil settlement that Metro was forced to make with the victim’s widow, Mr. Taylor has spent most of the past 31 / 2 years on the transit agency’s payroll (though not as a bus driver). That was the case until Thursday, when Metro terminated Mr. Taylor, two weeks after he pleaded guilty last month to a charge of negligent homicide in the 2008 accident. He faces up to three years of prison time.

In the Taylor case, the system, such as it is, failed spectacularly. His initial firing, just days after the accident, was overturned by a labor arbitrator. The police dropped the ball, ignoring the case for months. Prosecutors were silent. And the transit union blindly stuck up for Mr. Taylor, despite a checkered record that included three felony convictions as well as parole violations.

Metro shares the blame. When Mr. Taylor sought reinstatement through arbitration in 2009, the transit agency made a shockingly weak case, failing to present strong witnesses or evidence. This may have been because police were not forthcoming with evidence they had gathered. But according to several participants, transit officials were disinclined to make a strong case for Mr. Taylor’s negligence, fearing they risked undercutting their own defense in the lawsuit brought by the Tabor family. Unsurprisingly, the arbitrator overturned Mr. Taylor’s firing.

Metro says that it now has more muscular screening procedures to check the background of job seekers and that an applicant with Mr. Taylor’s record would not be hired today. Richard Sarles, Metro’s general manager, says that the agency has also strengthened its accident investigations so that, in theory at least, it can make firings stick.

Mr. Tabor’s senseless death was a tragedy for his family; the follow-up was a disgrace for police and prosecutors and a black mark for Metro and the transit union. All of them shared a responsibility to look out for the public, but none of them did. Now, at last, with Mr. Taylor’s guilty plea, there is a measure of justice. Let’s hope it serves as a lesson for the future.