As the former mayor of the western town of Tiquecheo from 2008 to 2011, Gorrostieta -- who survived two earlier assassination attempts -- was reportedly considered a high priority target for some Mexican drug cartels.
In 2009, unidentified gunmen ambushed her car as she was traveling with her husband, Jose Sanchez. Sanchez died of injuries he sustained in the attack.
Three months later, Gorrostieta was seriously injured in another attack, for which she said she did not understand why she was a target, but she thanked supporters and said she would continue to fight for her ideals.
"I will rise up again as many times as God allows me to so that I can keep on seeking, fighting for, and working out plans, projects and actions for the benefit of the people, especially those most in need," Gorrostieta, who was also a medical doctor, said after one of the unsuccessful attacks against her.
A story published on Tuesday in the leading newspaper El Universal describes Gorrostieta's city of Tiquicheo as one where the local drug trade calls the shots and, citing unnamed sources, may have factored in its politics.
Investigators are not ruling out any possible motives -- political, personal or criminal -- in her killing, the state's deputy attorney general, Marco Aguilera, told CNN.
Further reporting done by the news outlet reveals that the investigation is focusing on the the 11 months of Gorrostieta's life since she left office and whether there is anything that indicated impending danger.
While drug cartel violence has been known to affect Mexican officials and journalists, there have reportedly been calls for the Mexican government to do more to increase their security.
Fox News reports that more than 20 Mexican mayors have been killed in the six years since President Felipe Calderon declared war on drug traffickers.