Mexican prosecutors are investigating claims that a woman who killed two bus drivers last week in a northern border city was seeking revenge for alleged sexual abuse of female passengers.
The claims made in an email from the self-styled "bus driver hunter" echoed deeply in Ciudad Juarez, which has a grim history of sexual violence against women aboard buses.
A woman wearing a blond wig - or dyed hair - boarded one of the school bus-style vehicles that serve as transport in Ciudad Juarez on Wednesday morning. 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.
Over the weekend, media outlets began receiving 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 Juarez, across the border from El Paso, Texas. "I am the instrument of vengeance for several women."
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.
Authorities have not verified the authenticity of the email, or of a Facebook page set up under a similar name on August 31.
But Arturo Sandoval, spokesman for the Chihuahua state prosecutors' office, said the vigilante claim is considered one of the working hypotheses 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," Mr Sandoval said.
The government announced it will put undercover police aboard some buses and conduct weapons searches to prevent further killings, and said a city-wide search for the suspect is already on.