Mexico City - A series of murders targeting families, including children, rocked Mexico in recent weeks, signaling that drug gangs were willing to break an unspoken code of honour within the criminal underworld.In total, 34 people have been killed, including several women and 10 children in three regions since early July.Last month, 19 people, including eight children, from three different families were gunned down in less than a week in Ciudad Victoria, the capital of the northeastern state of Tamaulipas.Key routeAuthorities suspect that those massacres were linked to disputes between rival gangs in Tamaulipas, a region that has been besieged by drug cartel violence for years.Seven shark fishermen from the same family were killed in the southern Pacific coast state of Oaxaca on July 18.Authorities suspect it may be linked to illegal activities at sea. The Pacific is a key route for drug trafficking.The most recent massacre came on Saturday, when seven people from the same family, including two children, were shot dead in a small town in southern Guerrero state.While the motive is unknown, gangs are fighting for control of opium poppy production in the region.The modus operandi indicates that all these killings were linked to turf wars between criminal organisations that are the remnants of cartels that have splintered, said Raul Benitez Manaut, a security expert at the National Autonomous University of Mexico. Such gangs "no longer respect families, wives and children," said Benitez Manaut.A police agent investigating the slaughters in Tamaulipas said there used to be "a code of honour in which family was untouchable" in the old days of large cartels led by veteran capos."Now, in these modern times, this code is finished," said the agent.Criminal cellsThe Gulf and Zetas drug cartels have been fighting in Tamaulipas for years, but several of their leaders have been arrested or killed.Violence in Ciudad Victoria is blamed on offshoots of the Zetas known as the Old School and the Cartel of the Northeast.Experts warn that the vendettas between criminal cells may rise as family killings continue.Mexico's paltry record at putting criminals behind bars encourages gangs to kill without fear of consequences, analysts said.Only 1% of crimes in Mexico lead to convictions, according to a 2016 study by the University of the Americas in Puebla state.The spate of family killings "is more evidence of the impunity and lack of co-ordination to deal with or contain crime," said Javier Oliva, another prominent security expert."You can murder entire groups, including minors and women without getting justice immediately," Oliva said.