CIUDAD JUÁREZ, Mexico  The hit men moved in on their target, shot him dead and then disappeared in a matter of seconds. It would have been a perfect case for José Ibarra Limón, one of this violent border city’s most dogged crime investigators  had he not been the victim.

Mexico has never been particularly adept at bringing criminals to justice, and the drug war has made things worse. Investigators are now swamped with homicides and other drug crimes, most of which they will never crack. On top of the standard obstacles  too little expertise, too much corruption  is one that seems to grow by the day: outright fear of becoming the next body in the street.

Mr. Ibarra was killed on July 27 in what his bosses at the federal attorney general’s office consider an assassination related to a case he was investigating. As if to prove the point, less than a month later, one of the lawyers who had worked for Mr. Ibarra also turned up dead. Two days afterward, an investigator named to replace Mr. Ibarra insisted on being transferred out of Ciudad Juárez, Mexico’s murder capital.

The current prosecutor investigating Mr. Ibarra’s cases is working anonymously, his or her name kept secret by the government.