CAIRO (AP) ― The prosecution’s first witness in the trial of ousted Egyptian President Hosni Mubarak startled the court in a stormy session Monday, testifying that police were not ordered to fire on protesters in Cairo’s Tahrir Square in a contradiction of the prosecutors’ central claim.

The police general’s statement could damage the prosecution’s case that Mubarak and his security chief gave the green light to police to use lethal force to crush the uprising, during which at least 850 people were killed.

Prosecution lawyers were visibly stunned by the testimony of the witness, Gen. Hussein Moussa, and angrily accused him of changing his story from the affidavit he initially gave prosecutors.

Many Egyptians have been crying out for the conviction ― and even execution ― of the 83-year-old Mubarak to avenge not only the deaths but also the corruption, police abuse and other oppression during his nearly 30-year rule. If prosecutors fail to win a guilty verdict or end up with a conviction but a light sentence, there could be a heavy public backlash. The 10-hour session was raucous, with both supporters and opponents of the ex-president in the audience.

Relatives of slain protesters threw water bottles at the defendants’ cage where the ailing Mubarak lay in a hospital gurney, as he has in previous sessions since the trial began Aug. 3. They shouted, “Mubarak, you traitor” and “The people want to execute the ousted one” before court guards quieted the situation.

At one point, a Mubarak loyalist held up a poster of the former leader, prompting furious arguments between the two sides’ lawyers that devolved into shouted insults then into outright fist-fights. One lawyer beat another with his shoes until the judge called a brief adjournment to calm things down.

Outside the Police Academy where the trial is being held, protesters’ relatives who had been prevented from entering the court pelted police with stones and tried to push their way into the compound.

They railed against a decision by the judges to halt live TV broadcasts of the trial, which many Egyptians complain is cheating them of their chance to see Mubarak prosecuted.

Moussa was the opening witness for the prosecution as the trial moved for the first time into testimony after several sessions dominated by procedural issues. The next session was set for Wednesday.

Mubarak is charged with corruption and with complicity in the killings of protesters during the 18-day uprising that led to his Feb. 11 fall from power. On trial with him are his sons, Gamal and Alaa ― on the corruption charges ― and his former Interior Minister Habib el-Adly and six top police officers, facing the protester killings charge, which carries a possible death sentence.

Prosecutors claim that Mubarak and el-Adly, his highest ranking security chief, issued the orders allowing use of lethal force against the peaceful protesters.

Gen. Moussa, who headed the communications unit of the Central Security Forces, was a key piece of their case. Before Monday’s session, prosecutors said Moussa would pin orders to open fire on protesters with live ammunition directly to el-Adly ― and by implication to Mubarak.

But when the judge asked Moussa on the stand if he knew whether el-Adly issued such orders, Moussa replied, “No, I don’t know,” according to Mohammed Damaty, a lawyer representing the victims’ families, and human rights activist Gamal Eid, who tweeted from the courtroom.

Moussa said it was Gen. Ahmed Ramzy, another of the defendants, who gave the order. “Anybody else?” the judge asked. “No,” Moussa answered.

Moussa said live ammunition was used only against protesters who tried to attack the Cairo security headquarters, police stations and prisons. He said that in Tahrir Square, the epicenter of the uprising where witnesses and prosecutors say police snipers opened fire, he said security forces used only tear gas, water cannons and rubber bullets.

One of the prosecution lawyers, Mustafa Khater, confronted Moussa on the stand, saying that in early questioning by prosecutors he testified that el-Adly himself gave the order to use live ammunition and that it had been used against protesters in front of the ruling party headquarters.

Visibly angry, Khater said Moussa had said in his affidavit that el-Adly’s Interior Ministry deployed a special force armed with automatic weapons under orders to use “any means” to crush protests.

“I have no answer,” Moussa replied simply to Khater.

Prosecutors then tried to chip at the credibility of their own witness, getting him to admit that he had been sentenced to two years in prison for “damaging evidence and records.” Moussa was handed the sentence for deleting audio records of el-Adly’s conversations with top aides, a security official told AP.

Damaty, the lawyer for victims’ families, accused Moussa of “twisting the truth.”

“It was clear that the defendants have put pressure on him and that he changed his testimony,” he said.

Two other police officers who testified later in the session echoed a similar line as Moussa. They said there were no orders to kill the protesters, instead, “the orders were to open fire in the air or at their legs,” Capt. Bassem Hassan, according to Eid’s tweets.