The little buses looked like any others as they rattled down the dirt streets of El Alto, collecting people headed to work in the pre-dawn chill.
But authorities say they were death traps, employed by a murderous band to harvest victims who would be strangled for what little they possessed.
Police are blaming the band for at least 69 killings and say dozens more victims survived the stranglings and were left for dead in isolated stretches of the working class city of 1 million people on the arid plateau above Bolivia's capital.
"This kind of assault came about because people, of necessity, take whatever transport they can get," said police Col. Felix Rocha, chief of Bolivia's criminal police.
Gang members would ride the minibuses posing as passengers, police said. When their prey boarded and dropped into a seat, they were strangled with a rope or scarf and stripped of valuables that often amounted to little more than a cell phone and the clothes on their backs, Rocha said, the bodies dumped in remote districts of this city inhabited chiefly by indigenous migrants from the countryside.
A 64-year-old man who said he survived a Feb. 5 attack by the band recounted leaving his house at 4 a.m. on his way to the bank were he collects his monthly pension.
He said he confidently boarded what he thought was a public transit minibus because, as usual, his 25-cent fare was collected by "a cholita," or indigenous woman.
"They had me sit in the front and all of the sudden I felt a blue scarf tightening around my neck. I fought back but they hit me in the ribs" and face and he fell unconscious, said the man, who asked to be identified only by first name, Macario, because he fears for his safety.
"I woke up later in a dumpster," Macario added. Gone were his cell phone and the equivalent of $55 in the local currency, bolivianos.
Police last week announced the arrest of eight alleged members of the band, ranging in age from 30 to 45 and including the woman, whom they identified as Yuli Gutierrez Jimenez.
Rocha said police seized four 14-seat minibuses used by the band, two of the white, one gray and another beige.
He said most of the killings occurred between 4 a.m. and 6 a.m. when public transport is relatively scarce and only 400 police are on duty in the entire city, which is mostly unpaved and where many neighborhoods lack running water and electricity.
Rocha said the band is believed to have killed 69 people whose bodies were found over the past 13 months, though prosecutor Santos Valencia said investigators are still trying to determine if the group was responsible for all those killings.
The gang appeared to have been less than thorough because more than 70 people told police they had survived attacks after recognizing gang members in local media reports, Rocha said. Other such bands are known to exist, but the minibus gang seems to have been the best organized and most methodical, he added.
Its alleged leader, identified by police as 33-year-old Julio Edwin Valdez, was arrested last week by heavily armed, masked police wielding assault rifles.
Also captured was Galo Mamani, identified as the bus's driver. Prosecutors say the two face murder charges but offered few other details. The charges faced by the other suspects were not immediately clear.
Valencia told reporters that police found wallets and the clothes of victims in the homes of the detained. Authorities did not say how they tracked down the alleged criminals.
A judge, Karina Barea, ordered all eight arrested held in preventative detention pending formal charges.
Rocha said police were investigating whether the group also was involved in the recent strangulation murders of several taxi drivers whose vehicles were stolen.
Across Latin America from Lima, Peru, to Mexico City, taxis that are commonly used by criminals to commit armed robberies. A driver, often in an unregistered cab, will pick up a passenger and then stop unexpectedly along with way so that burly accomplices armed with knives or a gun can climb in.
The people of El Alto, located on an Andean plateau at 4,000 meters (13,325 feet) and home to La Paz's international airport, are mostly Aymara, the ethnic group of President Evo Morales.
Many are fed up with the teeming city's insecurity, and hundreds marched last Wednesday and Thursday to demand greater police protection.
"We don't let our children go out late at night," said Juan Quispe, a former miner. "The police only come around to pick up to bodies that criminals toss into the streets."
A leader of El Alto's dominant grass-roots civic group told The Associated Press on Monday that it had received complaints from nearly every one of the city's 10 districts of killings by bands known as "cogoteros," or stranglers.
"These cogoteros take advantage of the majority of workers here, who leave their homes early in the morning to go to work," said Claudio Luna, vice president of the Federation of Neighborhood Councils.
He said neighborhood councils were planning to organize joint patrols with police to protect workers in the wee hours.
Associated Press writer Frank Bajak contributed to this report.