A longtime Castro foe turned over a new cache of weapons in Miami in the hope of reducing his prison sentence and that of an exile colleague.

BY JAY WEAVER

An ally of Cuban exile militant Luis Posada Carriles turned over a stockpile of illegal machine guns, dynamite and a grenade launcher to federal agents this week in a bid to reduce his prison sentence, several sources familiar with the arms surrender said.

Santiago Alvarez, a wealthy Miami developer convicted last fall on a weapons-conspiracy charge, arranged for the turnover of the new cache of firearms on Wednesday at his attorney's office in downtown Miami, sources said.

Alvarez and convicted co-defendant Osvaldo Mitat are seeking to reduce their respective four- and three-year prison sentences by one or more years. The unusual arms surrender has no connection to Posada's latest troubles with federal authorities.

The Alvarez stash consisted of dozens of machine guns, rifles, C-4 explosive, dynamite, detonators, a grenade launcher and ammunition, sources said. The cache was considerably larger than the nine illegal firearms seized by federal agents in late 2005 when Alvarez and Mitat were first indicted on weapons charges in Broward County.

Agents for the FBI and Alcohol, Tobacco, Firearms and Explosives collected the latest stash of weapons at the Miami law office of Silvia Piñera-Vazquez and Sofia Powell-Cosio. The lawyers were granted temporary immunity to surrender the firearms to federal authorities on behalf of their clients, Alvarez and Mitat. Piñera-Vazquez, who declined to comment for this article, personally delivered a letter to the U.S. attorney's office on Tuesday detailing the proposed weapons turnover.

The voluntary surrender was designed to take the firearms off the street and boost the defendants' chances of reducing their sentences.

Alvarez, 65, has been in federal custody since November 2005, as has Mitat, 64, a handyman who worked for him. To obtain reductions of their sentences, they must prove to prosecutors they have provided enough ''substantial assistance.'' Prosecutors would have to file the request in federal court.

Defense attorneys for Alvarez and Mitat have said their clients never had any designs to carry out an attack against the U.S. government. They say the men's goal was always to topple Cuban leader Fidel Castro.

PIPE BOMB FOUND

The weapons turnover occurred just days after an FBI informant -- who has informed on Posada, Alvarez and Mitat -- reported that he discovered a pipe bomb under his pickup truck in Hialeah on Sunday. Miami-Dade police officers detonated the device at the Hialeah police station. They found wires and gun shells among the bomb scraps. The FBI launched a probe but declined to comment.

Attorneys for Alvarez, Mitat and Posada said their clients -- all in federal custody in Texas -- were not involved in the pipe-bomb incident. They expressed serious doubts about the credibility of the informant, Gilberto Abascal, whom they have characterized as a ''double agent'' for the FBI and for Castro's government.

Lawyers for Alvarez and Mitat have been negotiating with the U.S. attorney's office since their sentencings in November to turn over the new weapons cache, sources familiar with the case told The Miami Herald.

COMMON THREADS

Intrigue surrounding the weapons surrender could not be greater. Last September, Abascal was the main federal witness who helped convict Alvarez and Mitat on weapons-conspiracy charges in South Florida. Abascal was also the primary witness in last week's federal indictment of former CIA operative Posada on fraud offenses.

A federal grand jury in El Paso, Texas, charged Posada, 78, with lying about how he sneaked into the United States in March 2005.

The same grand jury also charged Alvarez and Mitat with contempt of court for refusing to testify about Posada's entry into the country. Three other associates have been charged with contempt in the case.

Posada has long maintained that he entered the United States by crossing the Mexican border with the assistance of a migrant smuggler, not by sea -- as prosecutors now allege.

Abascal said Posada entered the country on a shrimping boat called Santrina, which was manned by Alvarez, Mitat and others, including the informant himself. Abascal said the Santrina crew picked up Posada on the Mexican island of Isla Mujeres and transported him to the United States.

By charging Posada, the Justice Department signaled its willingness to target a man who has been in investigators' cross hairs since 1997, when he first was suspected of masterminding a series of deadly tourist-site bombings in Cuba.

Federal agents began zeroing in on Alvarez in May 2005 when he helped Posada emerge from hiding before his arrest for entering the country illegally. That November, Alvarez and Mitat were charged with stashing machine guns, a silencer and a grenade launcher in a Lauderhill apartment complex that belonged to Alvarez.

The defendants' attorneys claimed Abascal, who called federal agents on the way from Broward County to Miami-Dade, set up his former friends.

Although prosecutors never accused the two men of planning to use those firearms in an attack against the Cuban government, they intended to introduce evidence at trial that showed Alvarez had financed a failed 2001 incursion against Castro, among other paramilitary activities. Plea deals came on the eve of trial.

Court records also show that federal and Bahamian authorities recovered a large cache of weapons and explosives hidden on Guinchos Cay in August 2005 -- ``an operation conducted after agents learned that Alvarez was storing and maintaining this arsenal.''