Had he switched sides to cooperate with the United States government?
On Tuesday, Mr. Zarrab gave a stunning answer, appearing as the government’s star witness in the trial of Mr. Attila, the Turkish banker who had been charged with him.
Through three days of often-compelling testimony, Mr. Zarrab has appeared composed, has maintained a respectful tone and has rarely looked uncomfortable answering questions. His testimony about how he had carried out the scheme, working with bankers and a government minister, sent political tremors through Turkey.
Hints emerged about why Turkey’s president was so interested.
Ever since Mr. Zarrab’s arrest in March 2016, Turkey’s president, Recep Tayyip Erdogan, has repeatedly condemned the prosecution and seemingly tried everything to have the case dismissed.
Mr. Erdogan claimed there were “malicious” intentions behind the prosecution, and he raised the case with American officials, including Mr. Trump, in a phone call in September.
“We have to seek justice, for he is our citizen,” Mr. Erdogan said of Mr. Zarrab more than a year ago.
But in his testimony this past week, Mr. Zarrab all but implicated Mr. Erdogan in the alleged scheme. He testified that Zafer Caglayan, then the economy minister, had told him in 2012 that Mr. Erdogan, who was prime minister at the time, had personally ordered that two Turkish banks be allowed to participate in the sanctions-busting activity.
Mr. Zarrab also said he had paid Mr. Caglayan tens of millions of dollars in bribes. Mr. Caglayan is one of the seven defendants who remain at large.
Turkey was abuzz.
Turkey has been gripped by the trial, with its cast of rich and powerful characters and its enormous sums: billions of dollars in Iranian oil money and bribes in the tens of millions of dollars, allegedly paid to the former economy minister.
The Turkish government tried to head off negative news coverage, denouncing the trial in the days before it began as a plot against the government and against Turkey itself.
Justice Minister Abdulhamit Gul said the evidence had been fabricated by followers of the cleric Fethullah Gulen — who was accused of fomenting last year’s failed coup against Mr. Erdogan — and that a 2013 Turkish police investigation into the matter had been dismissed for that reason. Mr. Gulen lives in self-imposed exile in Pennsylvania.
In Turkey’s increasingly authoritarian climate — a state of emergency has been imposed for more than a year — newspapers and television channels have largely followed the government line, describing Mr. Zarrab as a hostage and his decision to cooperate with the United States prosecutors as forced.
Television chat shows discussed at length his appearance in tan jail attire on the first day of the trial. Only one newspaper, the independent daily Cumhuriyet, dared lead with the most momentous detail: Mr. Zarrab’s statement that Mr. Erdogan had ordered two banks to be included in the scheme.
But social media was abuzz with the case all week, and Turks followed live feeds from reporters and online news outlets covering the trial in English and Turkish.
The scale of the bribes that Mr. Zarrab said he paid the former minister drew bitter jokes.
“The bribe was 45 or 50 million euros,” one user wrote on Twitter. “I would have to work 11,750 months. That makes nearly a thousand years. 1,000. 1,000!”
Burak Acerakis, who campaigns for education for children with Down syndrome, wrote, “With only 2.6 percent of the bribe taken by Caglayan, 36,000 children with Down syndrome would be able to have pre-education therapy for five years.”
The judge said he would excuse a drowsy juror.
Not all the testimony has been riveting, or so it seemed for at least one of the 12 jurors hearing the case. Late on Friday, after Judge Richard M. Berman had excused the jury for the weekend, he announced that he was going to dismiss one juror from the case.
His offense? Sleeping.
“It was my observation,” the judge said, “that one of the jurors in my direct line of sight has been sleeping almost the whole trial.”
Judge Berman said that the man “seemed like a very nice fellow,” and he noted that during the jury selection, when he had asked the man what he liked to do in his spare time, the answer was, “Sleep.”
“That, maybe, should have told us,” Judge Berman noted.
He said he would notify the juror that he had been excused. Several alternate jurors have been selected, and one will move onto the regular panel.
Judge Berman made it clear that he believed the issue of staying alert through testimony was an important one.
“I just don’t think a juror can perform his duties — him or her — unless they pay attention to what’s going on in the courtroom,” he said, adding, “Today to me was the icing on the cake.”
The juror had been “really sound asleep,” Judge Berman added. “Not just dozing.”