Mexican authorities are investigating the murder of two bus drivers in Mexico last week, this follows claims that the woman who was responsible was seeking revenge for the alleged abuse of female passengers.

Emails claiming to be from "Diana the hunter of bus drivers" were sent to media organisations, similar messages were also posted on social media sites over the weekend.

Suffered in silence 

"I myself and other women have suffered in silence but we can't stay quiet anymore," the email read.

"We were victims of sexual violence by the drivers on the night shift on the routes to the maquilas (factories).

"I am the instrument of vengeance for several women."

However, police have not verified the authenticity of the emails, or of a Facebook page set up under a similar name.

A woman wearing a blonde wig boarded a bus in on Wednesday morning, she shot the driver in the head with a pistol and then fled the scene. 

The next day another driver on the same route was killed, apparently by the same woman.

The newspaper 'Diario de Juarez' reported that a witness quoted the killer as telling the second victim, "You guys think you're real bad, don't you?" before shooting him.

Theory taken seriously

Arturo Sandoval, a spokesman for the state prosecutors' office said they were taking the female vigilante theory seriously and that undercover police are being put on some buses.

Detectives have stated that they have a sketch of the killer.

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

Ciudad Juarez, located just over the border from El Paso in Texas.

Ciudad Juarez

The city is notorious for gang crime and has a history of horrific violence against women.

In the 1990s and 2000s more than 100 women were killed after boarding buses in the city.

Their bodies were often found later, raped, strangled and dumped.

Several bus drivers were arrested in connection with those killings, however the cases against them always appeared weak.

One driver had his conviction overturned, and his co-defendant, another bus driver, died in prison before sentencing.

There is now speculation on whether this female vigilante could be seeking revenge on behalf of these women.