A Mexican woman arrested and jailed last weekend in connection with the killing of a university professor was freed here after family and friends launched a campaign for her release on social-networking sites.

Mexico City District Attorney Miguel Angel Mancera told reporters that authorities have dropped all charges against Mariel Solis Martinez, a 23-year-old student at the National Autonomous University of Mexico, due to lack of evidence.

She was arrested for her alleged role in the killing of university professor Salvador Rodriguez, who was slain by two people in 2009 after withdrawing money from an ATM machine and resisting their attempt to rob him.

Solis was taken into custody and jailed in Mexico City after Eduardo Lopez Herrera, sentenced to 113 years in prison for the crime, identified her in a photo array as the woman on the ATM's security video.

"It's hard to understand how the word of someone, a murderer, is worth more than the word of someone who, I'm not saying I'm a saint, but I'd never commit a crime, any crime," Solis said in a radio interview after being released on Thursday.

Her attorney, Rafael Heredia, said it was shocking that "that criminal who killed his wife at a prison and was sentenced to 100 years" for murdering Rodriguez is believed when he makes a false accusation.

Heredia told MVS radio that pressure from Solis' family and friends, who launched a campaign for her release on social-networking sites, was the key to her recovering her freedom.

Solis' ordeal came just months after the release in Mexico of "Presunto culpable" (Presumed Guilty), a documentary about a young man, Antonio Zuñiga, who was wrongly convicted of murder and sentenced to 20 years in prison based on a false accusation.

Zuñiga was imprisoned for nearly two-and-a-half years until he was finally exonerated and freed with Heredia's help.