(March 6, 2007)--The head of a notorious prison gang who allegedly approved more than a dozen killings in San Antonio during the 1990s heads was put to death just after 6 p.m. Tuesday in Huntsville. Mexican Mafia chief Robert Perez was executed for the Alamo City hits on Jose Travieso and James Rivas 13 years ago. He was the seventh prisoner Texas has put to death this year and the first of two in as many nights. Appeals were exhausted for Perez. A lawsuit on his behalf challenging the Texas execution procedures was dismissed in a Houston federal court last...