More than 750 troops and federal police officers along with tanks and helicopters on Friday seized control of the nation's top maximum-security prison, where drug kingpins have managed to carry out killings and conduct business in recent months. The takeover came a day after the infamous leader of the so-called gulf cartel, Osiel Cärdenas, organized prisoners to protest the tightening of security at the prison, La Palma. Guards had clamped down on the freedom of inmates after a gunman killed one of Mr. Cärdenas's underworld enemies as he sat in a visiting room on New Year's Eve. It was the second drug-related killing inside the prison in three months.The killing rocked the administration of President Vicente Fox and prompted the ouster of five prison officials this month. The incident also showed just how much influence Mr. Cärdenas and the leader of the Tijuana cartel, BenjamÃÂn Arellano, had over prison officials, through bribes and threats, federal officials said. "We were conscious of the need to recover control," said Rubén Aguilar, a spokesman for Mr. Fox. "And we needed to retake control by force."