Both brothers were sentenced to life in prison for the attacks on the California Highway Patrol troopers.

Throughout many court hearings, no audio had ever surfaced of the first encounter between Morin and Escobar, who only speaks Spanish.

In preparing for this week’s trial testimony, Morin was looking for audio of a Miranda warning delivered by California detectives investigating the attempted murder of the highway patrolmen.

In one of dozens of boxes of evidence, Morin found an unmarked, undated cassette. It featured about eight minutes of a Spanish-language exchange between Morin and Escobar.

The retired detective immediately told prosecutors. Assistant State Attorney Reid Rubin told the judge Tuesday.

The discovery was a surprise to Rubin, the case’s lead prosecutor.

“I didn’t think it has been played in any prior trial, or disclosed” to the defense, Rubin told the judge.

Whether previous prosecutors or the detectives knew of its existence remains unclear.

But if the tape indeed shows that Escobar invoked his right to remain silent during his first encounter with Miami detectives, then the confession three days later is not valid, Reizenstein told the judge.

Reizenstein asked for the rest of Tuesday to get an exact transcription and translation of the tape before he and Escobar decide whether to accept the life-in-prison plea.

If Escobar does not accept the plea offer, his lawyers can ask Circuit Judge Leon Firtel to throw out the confession, and Morin likely would have to testify about the tape at a hearing.

His confession is a key element in the state’s case against him. If the confession survives a legal challenge, defense lawyers would likely attack Morin’s credibility.

“No confession, no case,’’ Reizenstein told jurors last week during opening statements. “This case boils down to that simple proposition.”