MEXICO CITY (Reuters) - A journalist was shot dead on Tuesday in the Mexican state of Veracruz as he attended a Christmas celebration at his son s school, the latest murder in the country s deadliest year on record for media workers. Gumaro Perez, 35, who regularly wrote about security and drug trafficking, was shot at four times and killed in the Acayucan municipality, becoming the third journalist killed in the state, and Mexico s twelfth, this year.  Perez worked for Golfo Sur and Voz del Sur, among other media organizations.  We re in shock, waiting for them to hand over the body and see what we re going to do together with his family,  said  journalists  group Asociacion de Periodistas Independientes de Acayucan, to which Perez belonged.  A lone gunman entered Perez s 6-year-old son s classroom, where the Christmas celebration was being held, and fired at Perez, the group said, citing witnesses.  Roberta Jacobson, the U.S. ambassador to Mexico, condemned Perez s death in a post on Twitter, writing that she was  outraged by the death of another brave journalist in Mexico.     You don t kill the truth by killing journalists,  she added. At least 65 media workers were killed worldwide doing their jobs this year, including 50 professional journalists the organization Reporters Without Borders said on Tuesday, adding that Mexico is one of the most dangerous places to be a journalist. [ Since 2000, at least 111 media workers have been killed in Mexico, with 38 deaths since Enrique Pena Nieto became president in December 2012, advocacy group Article 19 says. 