Ethan Elder, father of Finnegan Lee Elder, arrives at Fiumicino Rome Airport Wednesday, July 31, 2019. Finnegan Lee Elder, 19, is suspected of being the one who stabbed Carabinieri officer Cerciello Rega and is detained in Rome with Gabriel Christian Natale-Hjorth, 18, who is suspected of assaulting another officer. (AP Photo/Gregorio Borgia)

ROME (AP) — The father of one of the Americans detained in the fatal stabbing of an Italian police officer said Wednesday that his 18-year-old son insists he didn't know his friend had a knife and "can't come to terms with what happened."

Fabrizio Natale issued a statement through a lawyer after visiting his son, Gabriel Christian Natale-Hjorth at a Rome prison, a meeting Natale described as "very tough for both" of them.

"We are very upset by the predicament he's in, but we are all fully convinced of his innocence," the father said in the statement.

Finnegan Lee Elder, 19, a former high school classmate of Natale-Hjorth's, also is in custody for the slaying early Friday of Carabinieri Deputy Brigadier Mario Cerciello Rega,

Prosecutors say Elder has confessed to knifing Cerciello Rega, 35, who was stabbed 11 times and died at a hospital. They have said Natale-Hjorth was suspected of fighting with the officer's partner at the time.

Cerciello Rega had recently returned from his honeymoon and not been scheduled to work when he and the partner were sent out in plainclothes to work a case involving an alleged extortion attempt over a drug deal, police have said.

The two Carabinieri went to meet people who demanded 100 euros ($112) and a gram of cocaine in exchange for returning a knapsack to an Italian man who was their intermediary for a drug deal that wasn't consummated, according to prosecutors.

Italian authorities allege the two teenagers from California were the ones who showed up for a scheduled rendezvous. They allege Elder attacked Cerciello Rega with a military-style attack knife he had brought with him from the United States.

Natale said his son "never imagined there would be a confrontation and did not know his friend was armed."

Prosecutors said police found the knife used in the slaying hidden in the dropped ceiling of the Americans' hotel room.

Under Italian law, both the defendant who materially carries out a killing and others involved in the crime can each be charged with murder.

Elder's father arrived in Rome earlier Wednesday, accompanied by a family friend who is an experienced lawyer, the teen's uncle, Sean Elder said by email.

Asked if his nephew collected knives or used them for a sporting activity, Sean Elder replied that "his mother says she had seen a knife similar to those other teens in his circle had."

Investigators allege the two officers were attacked immediately after they identified themselves as Carabinieri. The teens have contended that didn't realize the men were police officers.

According to court documents, Elder told prosecutors during his interrogation he thought he was being strangled in a scuffle with the officer. But prosecutors said there were no signs of physical injury on either teen.

Fabrizio Natale described his son as a "normal" teenager who was studying to become an architect.

"He is devastated by the Carabinieri's death, and I, as a father, cannot help but feel the grief of (Cerciello Rega's) family," Natale said.

This picture released by Italian Carabinieri during a press conference in Rome, Tuesday, July 30, 2019, shows the knife used to stab Carabinieri's officer Mario Cerciello Rega early Friday. Two American teenagers were jailed in Rome on Saturday as authorities investigate their alleged roles in the fatal stabbing of the Italian police officer on a street near their hotel. (AP Photo/Andrew Medichini)
A police car stations in front of the Meridien hotel in Rome, where two suspects from California, Finnegan Lee Elder, 19, and Gabriel Christian Natale-Hjorth, 18, were arrested hours after Deputy Brigadier Mario Cerciello Rega, 35, was knifed 11 times to his death, Wednesday, July 31, 2019. (AP Photo/Paolo Santalucia)
In this photo released by Carabinieri, is portrayed officer Mario Cerciello Rega, 35, who was stabbed to death in Rome early Friday, July 26, 2019. Italian police said Saturday that two 19-year-old American tourists have confessed to fatally stabbing the Italian paramilitary policeman who was investigating the theft of a bag with a cellphone.
Ethan Elder, father of Finnegan Lee Elder, arrives at Fiumicino Rome Airport Wednesday, July 31, 2019. Finnegan Lee Elder, 19, is suspected of being the one who stabbed Carabinieri officer Cerciello Rega and is detained in Rome with Gabriel Christian Natale-Hjorth, 18, who is suspected of assaulting another officer. (AP Photo/Gregorio Borgia)
The lawyer of Finnegan Lee Elder, Roberto Capra, receives media attention as he walks out of the Meridien hotel in Rome, where two suspects from California, Finnegan Lee Elder, 19, and Gabriel Christian Natale-Hjorth, 18, were arrested hours after Deputy Brigadier Mario Cerciello Rega, 35, was knifed 11 times to his death, Wednesday, July 31, 2019. (AP Photo/Paolo Santalucia)
Carabinieri Colonel Lorenzo D'Aloia shows a picture of the knife used to stab Carabinieri's officer Mario Cerciello Rega, during a press conference in Rome, Tuesday, July 30, 2019. Two American teenagers were jailed in Rome on Saturday as authorities investigate their alleged roles in the fatal stabbing of the Italian police officer on a street near their hotel. (AP Photo/Andrew Medichini)
Carabinieri officer Mario Cerciello Rega's wife, Rosa Maria, holds in her hand a rosary as she touches the coffin containing the body of her husband during his funeral in his hometown of Somma Vesuviana, near Naples, southern Italy, Monday, July 29, 2019. Two American teenagers were jailed in Rome on Saturday as authorities investigate their alleged roles in the fatal stabbing of the Italian police officer on a street near their hotel. (AP Photo/Andrew Medichini)
The picture of Carabinieri's officer Mario Cerciello Rega is shown during his funeral in his hometown of Somma Vesuviana, near Naples, southern Italy, Monday, July 29, 2019. Two American teenagers were jailed in Rome on Saturday as authorities investigate their alleged roles in the fatal stabbing of the Italian police officer on a street near their hotel. (Ciro Fusco/ANSA via AP)
A police car stations under the Meridien hotel in Rome, where two suspects from California, Finnegan Lee Elder, 19, and Gabriel Christian Natale-Hjorth, 18, were arrested hours after Deputy Brigadier Mario Cerciello Rega, 35, was knifed 11 times to his death, Wednesday, July 31, 2019. (AP Photo/Paolo Santalucia)