Mexican authorities Wednesday announced the arrest of a key suspect in the attempted assassination of a state security chief whose convoy was attacked with grenades and more than 2,000 rounds of ammunition.

The suspect until recently was a police commander who also worked for the notorious drug cartel known as La Familia, authorities said.

Minerva Bautista Gomez, security chief for the state of Michoacan, survived the April 24 ambush. Two of her bodyguards and two passing motorists were killed.

Ramon Pequeno, head of the anti-narcotics unit of the federal Public Security Ministry, said in a news conference in Mexico City that Miguel Ortiz Miranda, alias "El Tyson," had been arrested Tuesday in Morelia, the capital of Michoacan. Ortiz directed operations in Morelia for the Michoacan-based La Familia, Pequeno said, including attacks on public officials, kidnappings and extortion.

Pequeno said the suspect also participated in a June 14 ambush outside Zitacuaro that killed at least 10 federal police agents, as well as the 2009 assassination of a senior public security official and decapitation of a state prosecutor.

In one of the most brazen attacks on a public official, Bautista was ambushed as her entourage left a state fair. The assailants used a truck to block a narrow highway passage and opened fire from two sides. Investigators recovered 2,700 spent shells and said 350 high-caliber bullets had hit her heavily armored SUV.

Ortiz told interrogators that the attackers left the scene believing that Bautista was dead.

"Tyson indicated that the attack was in response to changes made within the ministry that went against the interests of La Familia," Pequeno said.

Authorities' contention that Ortiz worked for La Familia while a member of the state security forces illustrates how deeply traffickers have penetrated regional governments. Bautista told The Times in a recent interview that as many as 100 police agents have been interrogated as possible suspects in the attack on her.

Ortiz joined the Michoacan police in 1999 and became commander of a special operations unit before retiring in 2008 after a murder warrant was issued against him, Pequeno said. Ortiz began working for La Familia in 2005, Pequeno said, after accepting a large bribe to release a detained gang member. He provided information to the cartel, alerting it to police movements and offering protection.

La Familia is a ruthless gang dedicated to the trafficking of methamphetamine. The gang has evolved in recent years as its leaders have tried to create a quasi-religious aura around the group. Pequeno said Ortiz described five days of indoctrination when he joined La Familia that included Bible-reading, self-help seminars and weapons training.

Ortiz also told authorities that La Familia recently joined forces with the Gulf cartel and other smaller gangs to fight the paramilitary Zetas. The Zetas were once allied with Gulf traffickers but are now battling them in several parts of Mexico, including the northern border state of Tamaulipas, where presumed drug hit men this week assassinated the leading candidate for governor.

On Wednesday, officials with the Institutional Revolutionary Party in Tamaulipas named the slain candidate's brother, Egidio Torre Cantu, to run in his place in Sunday's election.

wilkinson@latimes.com