Mexico City - The arrest of four police officers in a case that has unsettled Mexico City is tarnishing the image officials have tried to cultivate of the capital as a safe haven from the violence and police corruption that plague other parts of Mexico.
The four are among 18 people now in custody for what's become known as the Heaven case, named for the after-hours bar in an upscale part of the city where 12 young people were kidnapped in broad daylight on 26 May. Their bodies were found three months later in a mass grave on a ranch in rural Mexico State.
Security Chief Jesus Rodriguez Almeida told The Associated Press about the most recent arrest on Tuesday, saying the four officers had all been through the department's vetting process and had four to 11 years of service with the police.
He could not say whether they passed background checks, polygraphs and other tests, citing rules of confidentiality.
"We're not prejudging whether they're guilty or not," Almeida said.
The kidnap and killing shook the city's image as one of the safer areas of Mexico, relatively free of brutal, drug-related crime that has been common in border cities and other areas where cartels fight over transit routes and territory.
"What the Heaven case proves with total clarity is that police can pass the controls and polygraphs as if they were candy," said Gustavo Fondevila, a public security expert with Centre for Investigation and Teaching of Economics. "They have absolutely no problem and continue to work for organised crime."
Ricardo Martinez, a lawyer for the Heaven victims' families, said he was not surprised that police have been implicated. "There are both criminals and public servants involved," he said.
Almeida conceded that the arrests weren't good for the reputation of the police force, which has been touted as one of the best-trained and equipped in a country infamous for corrupt law enforcement.
Police officers are often arrested in high-profile crimes throughout Mexico.
In border states and along the Gulf coast, entire police forces have been dismissed for suspected ties to organised crime or inability to pass confidence tests.
But he called it a myth to say police are involved in all criminal activity, and said his department maintains a strong fight against corruption.
"Among police worldwide, there are officers who follow the law ... and those who turn away from the law, and have to face the legal consequences of their actions," Almeida said, noting that Mexico City's police force has 87 000 officers.
The Heaven kidnappings on a sunny Sunday afternoon a block from the US Embassy and the Paseo de Reforma, the city's equivalent of the Champs Elysees, have been attributed to a dispute between rival gangs over drugs sales in bars and nightclubs.
Prosecutors have said they believe one gang was exacting revenge for the slaying of a drug dealer in a bar in the trendy Condesa neighbourhood.
The first police officer, who was detained last week, worked in the Zona Rosa, the touristy area of bars and restaurants where the Heaven bar was operating, police said.
Two more officers are being held under house arrest while authorities investigate their alleged involvement.
Thirteen bodies in all were unearthed from the mass grave. A federal prosecutor who was not authorised to speak to the media said the 13th victim might have been someone who aided the kidnappers.
Meanwhile, Mexican media distributed a video on Monday taken by a resident and uploaded to YouTube that records a kidnapping, again in broad daylight, involving three people in police uniform.
A man is forcibly pulled out of a car and loaded into a passing pickup by three people in helmets and bullet-proof vests who later drive off on motorcycles. The alleged kidnapping happened in a central, normally quiet commercial and residential neighbourhood.
Almeida said it was not clear that the people appearing on the tape were actual police officers.
"Guaranteeing the integrity of the police is an ongoing process. Vetting is not enough," said Alejandro Hope, a security analyst and former member of Mexico's domestic intelligence service.
"Even in Mexico City, where there is probably a better police force than anywhere else ... even here there's a completely dysfunctional police system."