Ethan Elder, centre, father of Finnegan Lee Elder, arrives at Fiumicino Rome Airport on Wednesday. Photo: AP Photo/Gregorio Borgia.

Rome – Both American teens jailed in Rome in the fatal stabbing of an Italian police officer now have private lawyers and family members in Italy.

Ethan Elder, father of Finnegan Lee Elder, arrived at Rome's airport on Wednesday on a flight from California. He didn't respond to questions shouted by reporters.

Investigators contend that his 19-year-old son stabbed Carabinieri Deputy Brigadier Mario Cerciello Rega 11 times with a military-style attack knife early on Friday near the hotel where he was staying with his friend. 

According to court documents, Elder told prosecutors during his interrogation that he thought he was being strangled in a scuffle with the officer.

But prosecutors say there were no signs of physical injury on either teen.

Under investigation along with Elder is his travel mate, Gabriel Christian Natale-Hjorth, 18, also from California. Natale-Hjorth's lawyer, Fabio Alonzi, said the teen's family visited him on Wednesday.

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

A day earlier, Elder's mother, in San Francisco, told private Italian TGCom24 that the family was "heartbroken" over the officer's death. She added that the teens' travel plans "came together at the last minute".

Prosecutors said police found the knife used in the slaying hidden in the dropped ceiling of the Americans' hotel room. Investigators said Elder told them he had brought the knife with him from the US.

According to prosecutors, the police officer and his partner, both in plainclothes, had gone to the site of a rendezvous that had been arranged by the teens who were trying to get 100 euros ($112) and a gram of cocaine in exchange for returning a knapsack they had stolen from an intermediary in a drug deal gone bad.

Investigators contend that Elder thrust the knife repeatedly into Cerciello Rega and that Natale-Hjorth punched and kicked the other officer.

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

AP