Blonde assassin allegedly shot two men dead in separate incidents, claiming to be 'instrument of vengeance for women'

Mexican prosecutors are investigating claims that a female vigilante killer is behind the murder of two bus drivers last week in the northern border city of Ciudad Juárez, apparently seeking revenge for the sexual abuse of female passengers.

An email from the self-styled "bus driver hunter" claiming responsibility for the assassinations echoed deeply in Ciudad Juárez, which has a grim history of sexual violence against women on buses.

On Wednesday morning a woman wearing a blonde wig – or sporting dyed hair – boarded one of the school bus-style vehicles that serve as transport in the city. She approached the driver, took out a pistol, shot him in the head and left the bus.

The next day, apparently the same woman did exactly the same thing to another driver on the same route. A witness quoted in Diario de Juárez claims to have heard the killer tell her second victim: "You guys think you're real bad, don't you?" before shooting him.

Over the weekend, media outlets started to receive emails from the address "Diana, the hunter of bus drivers".

"I myself and other women have suffered in silence but we can't stay quiet anymore," the email said. "We were victims of sexual violence by the drivers on the night shift on the routes to the maquilas," a reference to the border assembly plants that employ many residents in Ciudad Juárez. "I am the instrument of vengeance for several women."

Authorities have not verified the authenticity of the email, or of a Facebook page set up under a similar name. But Arturo Sandoval, spokesman for the Chihuahua state prosecutors' office, said the vigilante claim is considered a working hypothesis in the crimes. There was no apparent robbery involved in the killings.

"Now that we have the email in the case file, it indicates that this could have been someone who had a run-in with a driver or one of his relatives," Sandoval said.

The government announced it would put undercover police aboard some buses and conduct weapons searches to prevent further killings, and said a citywide search for the suspect is already on.

"We have a police sketch of the suspect and we are looking for her," municipal police spokesman Adrian Sanchez said.

Many of the women murdered during a string of more than 100 eerily similar women's killings in Ciudad Juárez in the 1990s and early 2000s disappeared after boarding buses. Their bodies were often found weeks or months later, raped, strangled and dumped in the desert or vacant lots.

Several bus drivers were arrested in connection with those killings – one had his conviction overturned and his co-defendant, another bus driver, died in prison before sentencing.

The head of the Chihuahua Women's Human Rights Centre, Lucha Castro, said that perhaps the killer "or someone close to her suffered some abuse by one of these guys.

"It's a fact that there are sexual abuse cases on the bus routes, but it's no greater than women disappearing from the streets in downtown, in human trafficking rings."

She added: "The most tragic thing is that the public may never know what the truth is."