Some Mexican reports Monday about Martinez's capture mentioned his alleged ties to Hartley's killing. But his arrest drew national attention for his alleged connection to some of the region's most high-profile crimes, including the 2010 massacre of 72 migrants in Tamaulipas, in addition to other slayings, mass graves and large-scale prison breaks in northern Mexico.
Martinez is accused of leading the Zetas in the Mexican states of Tamaulipas, Nuevo Leon and Coahuila, authorities said. Mexican officials also said Monday that he is suspected in "the execution of more than 50 people by his own hands in different parts of the country."
Shortly after Hartley's death was reported, authorities surmised that the couple had stumbled into the middle of a drug transaction. Gonzalez, the Zapata County sheriff, has said there were reports of fishermen on the lake being warned away from the Mexican side as long as a year before Hartley's shooting.
Word has eked out about possible suspects in the case. But information on the investigation has seemed scarce.
Last year, Tiffany Hartley sued the State Department, the Justice Department and the FBI in an attempt to get answers and find out why no one had been brought to justice in her husband's killing. All three lawsuits were dismissed this year after settlements were reached, according to court documents.
But the case has remained unsolved.
"It didn't happen in the United States," Gonzalez told CNN last year, adding that Mexican authorities have "somewhat of a zero solvency rate, and a zero conviction rate."
"So unfortunately," Gonzalez said at the time, "this case may remain open forever, even though the information and the evidence may be there."