The case of the after-hours bar known as Heaven, where the 12 were abducted on May 26 in broad daylight, shook the city's image as one of the safer areas of Mexico, relatively free of brutal, drug-related crime. The bodies of the young victims were found in late August in a mass grave outside the city.
Authorities say the mass killing was part of a dispute between gangs that control drug sales on street corners and bars. Prosecutors have said they believe one gang was exacting revenge for the slaying of a drug dealer in a bar in the trendy Condesa neighborhood.
The Mexico City prosecutor announced Monday that two police had been arrested in the case, putting the total at three. Almeida on Tuesday confirmed the arrest of the fourth officer. The number of suspects in custody is now 18.
Ricardo Martinez, attorney for the victims' families, said he is not surprised that police are being implicated. "There are both criminals and public servants involved," he said.
Almeida admitted that the arrests affect the reputation of the police force, which was also considered one of the better in a country infamous for corrupt law enforcement. Police are often arrested in high-profile crimes in Mexico, especially along the border and in areas where drug cartels are fighting for territory. Mexico City authorities continue to insist that organized crime does not operate in the city.
Almeida said all four officers who were arrested had been through the department's vetting process, but he could not say for confidentiality reasons whether they had passed their background checks.
Thirteen bodies in all were unearthed from the mass grave. A federal prosecutor who was not authorized to speak to the media said the 13th victim may have been someone who aided the kidnappers.