(Reuters) - With federal prosecutors expected to rest their case against Joaquin “El Chapo” Guzman on Monday, lawyers for the accused Mexican drug kingpin have given few clues about how they plan to counter three months of testimony by more than 50 government witnesses.

FILE PHOTO: Joaquin "El Chapo" Guzman is escorted by soldiers during a presentation in Mexico City, Jan. 8, 2016. REUTERS/Tomas Bravo/File Photo

Among the tough choices they face are whether to call their own witnesses to try to undermine the prosecutors’ evidence, and whether Guzman should take the stand in his own defense. One of his attorneys said on Friday that they would not reveal the names of any witnesses unless they decided to call them.

“Similarly, we will not disclose Joaquin’s plans about testifying until the time comes to inform the court,” Guzman lawyer Eduardo Balarezo said in a statement.

Guzman, 61, the alleged leader of Mexico’s Sinaloa Cartel, was extradited to the United States in 2017. He has been on trial since November on charges of trafficking vast quantities of cocaine, heroin and other illegal drugs into the country. Prosecutors have called more than a dozen former cartel members to testify against him.

The main defense argument, as put forth by Guzman lawyer Jeffrey Lichtman in his opening statement, has been that the real leader of the Sinaloa Cartel is Ismael “El Mayo” Zambada, and that Zambada bribed the Mexican and U.S. governments to frame Guzman.

Guzman’s lawyers have discussed multiple potential witnesses with prosecutors in open court, and have filed a motion suggesting they might call an inmate in the U.S. prison system, but they have not publicly revealed any names.

Defendants in criminal cases are under no obligation to call any witnesses. Many defendants in organized crime cases do not, said defense lawyer Steven Boozang, who defended Boston mafia boss Francis “Cadillac Frank” Salemme in a murder trial last year. He said the decision depends on what exonerating evidence is available.

“It has to be reliable,” he said. “It has to be truthful.”

Elie Honig, a former federal prosecutor, said it could make sense for a defendant to call witnesses if they could offer the jury an alternative explanation of the evidence that proved a defendant’s innocence. But he said such witnesses can backfire if their testimony is not convincing.

Lichtman said evidence for the defense’s contention that Zambada framed Guzman would emerge from the prosecution’s own witnesses, but such testimony largely failed to materialize. Multiple witnesses described Guzman as either the boss of the cartel or an equal partner with Zambada. The most explosive allegations about bribery came when one witness said Guzman paid $100 million to former Mexican president Enrique Pena Nieto. Pena Nieto has denied taking any bribes.

In many cases, Honig said, the only viable defense strategy is to seek to undermine prosecution witnesses who have pleaded guilty to crimes and agreed to cooperate.

“Tell the jury, ‘You just heard a bunch of tales from a bunch of lying criminal scoundrels who simply want to please the government, and my guy is their meal ticket,’” he said.

Guzman’s lawyers have sharply interrogated cooperating witnesses about their past crimes. Under cross-examination, former Guzman associate Jorge Cifuentes admitted traveling the world on forged identification documents; his former communications technician Christian Rodriguez admitted not paying taxes on money the U.S. government paid him to cooperate; and Colombian kingpin Juan Carlos “Chupeta” Ramirez acknowledged taking part in dozens of murders.

In Guzman’s case, the strategy may have limits. Much of the evidence against him is intercepted electronic messages in which Guzman himself appears to discuss drug deals, and his lawyers have not so far challenged their authenticity.

Boozang said Guzman’s lawyers were sure to discourage their client from testifying himself, which would let prosecutors cross-examine him.

“Putting on the defendant, it’s almost never done,” Boozang said, adding that the prosecution “would most likely have a field day” with Guzman.

But the alleged cartel boss may ignore his attorneys. Numerous witnesses have described him as boastful and impulsive.

In recent years, Guzman has courted publicity, seeking to make a movie about his life and giving an interview to actor Sean Penn for Rolling Stone magazine in 2015. In a Brooklyn courtroom, he could find his biggest stage yet.