Two American teenagers have been implicated in an Italian policeman's murder and are being held pending formal charges, Italy's Carabinieri police force said Saturday.

The two, both 19 years old, "confessed their deeds" after an Italian paramilitary policeman was fatally stabbed in Rome on Friday while investigating the theft of a bag with a cellphone. Elder Finnegan Lee and Christian Gabriel Natale Hjorth are being detained for aggravated murder and attempted extortion, correspondent Seth Doane reports.

A 35-year-old newlywed Carabinieri officer, Mario Rega, was stabbed to death on a Rome street early Friday morning. The Carabinieri said their investigation reveals that shortly before the murder, the two young men stole a backpack from an Italian man, and then threatened him during a phone call that they would not return the backpack unless they were given 100 euros and a gram of cocaine.

Two Italian Carabinieri stand near a blood-stained street where their colleague, Carabiniere Vice Brigadier Mario Cerciello Rega, was stabbed to death by a thief in Rome, Friday, July 26, 2019. The murder happened a few meters away from a police station and in front of the Italian Court of Cassation. Paolo Santalucia/AP

The man reported the incident to the Carabinieri, who came to the meeting to stop the criminals. But a scuffle unfolded, and the Carabinieri officer was stabbed to death.

Law enforcement found the Americans in their hotel room at Le Méridien Visconti, ready to leave Italy. Police say they searched the room and found the murder weapon – a "knife of considerable size," hidden behind a ceiling panel.

Rome police officer Mario Rega was stabbed to death early Friday. CBS News

Populist politicians have taken to social media today railing against "foreign animals" being allowed in Italy.

Rega, the slain officer, was from Somma Vesuviana, Italy. He did volunteer work with the poor, accompanied sick people to Catholic shrines, and brought meals to the homeless at Rome's main station. His funeral on Monday will be at the same church where he was married just 43 days ago.

The two Americans are reportedly from California. A lawyer for one of the men was spotted arriving at Regina Coeli, the Rome jail where they are being held.

A preliminary hearing is being held to determine whether to formally charge them.