Organized crime in Mexico has targeted several politicians or their relatives for assassination.
In 2010, gunmen believed linked to one of the cartels in the neighboring state of Tamaulipas ambushed a convoy carrying the PRI gubernatorial candidate, Rodolfo Torre, killing him and four of his companions. Torre's brother then ran for and won the governorship.
Several months later, a former governor of the Pacific state of Colima was shot dead and another state official was wounded by a group of armed men.
A PRI state legislator-elect in the northern state of Sonora was shot to death last month outside his home by a man on a motorcycle the day before he was scheduled to take office. Prosecutors said they believed he was killed by his legally designated substitute, but PRI officials voiced doubts about the theory.
Jaime Serrano Cedillo, a 45-year-old state deputy from the PRI, was fatally stabbed last month in Nezahualcoyotl, a district that borders Mexico City, in what authorities called a domestic dispute with his wife.
Correspondents Adriana Gomez Licon and Michael Weissenstein contributed.