At 2:30 a.m. on Nov. 8, 1992, a band of armed assassins burst into a crowded discothèque in Puerto Vallarta, Mexico, looking for revenge. Drawing weapons from their coats, contemporaneous news reports said, the gunmen shot out the nightclub’s lights and then trained their fire on the reveling members of a drug gang called the Arellano Félix organization.

Six people died in the shootout that ensued, and chroniclers of Mexico’s brutal drug wars have long attributed the massacre to Joaquín Guzmán Loera, a young kingpin known as El Chapo, who was settling a score with the leaders of the gang — the brothers Francisco Javier and Ramón Arellano Félix. On Tuesday, federal prosecutors in Brooklyn claimed that Mr. Guzmán was indeed involved and said that they planned to tell the tale of the decades-old slaughter at his trial.

The gunfight — which took place, prosecutors said, as Mr. Guzmán was consolidating his control of smuggling routes as a rising power in the Sinaloa drug cartel — was mentioned in a 90-page government memo filed in the case on Tuesday. With the sprawling conspiracy trial set to begin in September, the memo was designed to list the crimes that Mr. Guzmán was believed to have committed, but were not specifically laid out in his indictment. Those were legion, the memo said, and included murders, acts of torture, kidnappings, prison breaks and an attempt to smuggle seven tons of cocaine in cans of jalapeños.

In the 15 months since Mr. Guzmán was sent from Mexico to New York, his prosecution has been bogged down in legal technicalities related to his extradition and in arguments about the harsh conditions of his confinement in the high-security wing of Manhattan’s federal jail. The government’s new filing was the first detailed account of the often gruesome evidence that prosecutors plan to present to the jury.