Rome, Italy (CNN) Blindfolding one of the two American teenagers accused of murdering an Italian police officer was "grave and unacceptable," Rome's chief prosecutor said Tuesday, but he insisted that the suspect's interrogation was still valid.

Gabriel Natale Hjorth,18, was pictured blindfolded , with his arms behind his back in a photograph leaked to Italian media over the weekend.

The image raised questions over the conduct of his interrogation at the hands of police, but Italian prosecutor Michele Prestipino told a news conference Tuesday that Hjorth was not blindfolded while he was being questioned.

Prestipino insisted that Natale and fellow murder suspect Finnegan Lee Elder, 19, "were interrogated by the magistrates in conformity with the law."

Hjorth's lawyer, Emiliano Sisini, had earlier told CNN that he did not know how long his client was blindfolded for, but said the incident took place before his interrogation.

Italian police officer Mario Cerciello Rega was killed in an altercation after a botched drug deal in Rome.

Carabinieri police officer Mario Cerciello Rega was stabbed to death Friday in a case that has gripped Italy.

Rega was attacked while attempting to recover a backpack allegedly stolen by Elder and Hjorth following a botched drug deal, police say.

Police allege that both Americans confessed to taking part in the assault, and say Elder confessed to murder in the interrogation on Friday.

Seven inch knife

New details of Rega's murder were revealed during the wide-ranging press conference held by Prestipino, Rome prosecutor Nunzia D'Elia, and Gen. Francesco Gargaro, of the Provincial Carabinieri Command.

An image of the seven-inch knife police believe was used to kill Rega was shown to reporters. The weapon was found stashed in a ceiling panel in the hotel room both suspects were staying in, police said.

brought to Italy from the United States by Gargaro told CNN on Monday that the knife wasbrought to Italy from the United States by Elder

Police say the knife used to kill Carabinieri officer Rega was found in the suspect's hotel room.

Elder recognized the knife police say is the murder weapon "as his own," according to court documents seen by CNN.

On Tuesday, prosecutor Nunzia D'Eli said both suspects had lawyers and an interpreter with them to make sure they could properly express themselves during their interrogations.

The teens were "in shock," and under the influence of alcohol, but they were otherwise in good condition, she said.

Their interrogations lasted a long time and the suspects were allowed to give their side of the story, rather than simply having to answer yes or no questions, D'Elia said.

"They were lucid in their answers, giving us detailed accounts," she said.

"At the beginning, the suspects were having a hard time understanding the gravity of the situation. So much that one (Hjorth) asked: is he really dead?" she said.

No weapon on slain officer

The incident unfolded Friday after the two US citizens approached a man about buying drugs, according to police. After being sold crushed aspirin instead of cocaine, officers allege that the Americans stole a backpack from the man.

The teenagers subsequently answered the owner's cellphone, which they had also taken, and told him "they would not return the backpack without 100 euros ($111) and 1 gram of cocaine," police said.

The owner of the stolen bag then contacted the police and two unarmed plainclothes officers -- Rega and his partner Andrea Varriale -- met the American suspects under the guise of retrieving it, police said.

Slain police officer Mario Cerciello Rega and his wife on their wedding day, less than six weeks ago.

Both Americans are accused of assaulting the policemen, who reportedly identified themselves as law enforcement officers during the meeting early on Friday morning. Elder is further accused of stabbing Rega 11 times before fleeing the scene, Gargaro told CNN Monday.

The two Americans were arrested Friday evening inside their hotel room, close to the scene of the stabbing. They are accused of aggravated murder and attempted extortion, police said.

During Tuesday's press conference, Gargaro said the slain officer was not carrying his weapon when he was stabbed.

"Only he [Rega] knows why he didn't have the weapon with him. It could have been forgetfulness. But that doesn't change the fact that he would not have been able to use it," Gargaro said.

He added that Rega, who had recently returned from his honeymoon, was hit in the abdomen area and it "was impossible for him to react," Gargaro said.

"Some of the stab wounds went right through his body; his stomach, his spine and so on," Gargaro told the press conference.

In these photographs released by the Italian Carabinieri, Gabriel Christian Natale Hjorth, right, and Finnegan Lee Elder, sit in their hotel room in Rome.

According to court documents, Elder and Hjorth have turned on each other and are accusing each other "reciprocally." Their stories are "absolutely in contrast" with one another, the documents said.

The court documents suggest that Elder had not understood that the two men who approached them were police officers.

Elder's appointed public prosecutor, Francesco Codini, said during his court appearance Saturday that his client "maintained his right to remain silent" in front of a judge.

Elder's family said in a statement on Monday that the US consul in Rome had been allowed to visit Elder briefly.

"We continue to gather facts about his case through his legal representatives. Meanwhile we are grateful that he has been provided medical care," the statement said.

"As always, our hearts go out to the family and friends of Officer Rega, who have suffered an unimaginable loss," the family added in the statement.

Italian police can legally hold suspects for an entire year without official charges.

Rega's coffin was draped with the Italian flag. His funeral was attended by hundreds of mourners.

Tuesday's press conference came a day after hundreds of mourners gathered to pay tribute to Rega at his funeral in his hometown of Somma Vesuviana, near Naples.

His casket was draped with the Italian flag as it was carried into the same church where he was married less than two months ago.

The service was also attended by Italian politicians, including Deputy Prime Ministers Luigi Di Maio and Matteo Salvini.