Are Mexico bus driver murders revenge for sex attacks on passengers? Mexican police probing the murder of two bus drivers are looking into claims the killings were revenge for alleged sexual abuse. Two drivers were killed last week in Ciudad Juarez , a city in northern Mexico near the US border that is considered one of the most violent in the world. Over the weekend media outlets received an e-mail from a woman claiming to be "the hunter of bus drivers." The messages - not yet verified as authentic by police - said the murders were revenge for female passengers being allegedly abused by night-shift drivers. It read: "I myself and other women have suffered in silence but we can't stay quiet anymore." On Wednesday a woman - with a blonde wig or dyed hair - shot the first driver in the head with a pistol, Associated Press reported. The next day the apparent same woman repeated the attack, this time reportedly saying before pulling the trigger: "You guys think you're real bad, don't you?" The Diario de Juarez newspaper reported the killer did not rob the victims. According to the alleged killer's message, many women became victims of sexual violence when they travelled by bus to work in factories across the border in Texas. Arturo Sandoval, spokesman for the Chihuahua state prosecutors" office, said the vigilante claim is considered one of the working hypotheses in the crimes. Ciudad Juarez has a history of sexual violence against women. In the 1990s and early 2000s more than a 100 women disappeared, their bodies found weeks later, raped, strangled and dumped. Several bus drivers were arrested in connection with the killings. One driver had his conviction overturned and his co-defendant, another bus driver, died in prison before sentencing. More about: Ciudad Juárez, Crime, Mexico