Two American teenagers have confessed to fatally stabbing a police officer in Rome on Friday, according to authorities.

Deputy Brigadier Mario Cerciello Rega was allegedly killed by the two American college students shortly after they had stolen a backpack from an Italian man and then tried to extort the victim for "100 euros and 1 gram of cocaine," according to a police statement.

The Italian man agreed to pay the Americans after reporting the extortion attempt to police. The authorities attempted to arrest the Americans when they showed up for the exchange, but a scuffle broke out and Rega was stabbed and killed, Italian police said.

Rega worked for the Carabinieri, Italy's paramilitary police corps, in Rome. A spokesman said the officer was dressed in plainclothes at the time of the stabbing.

The two Americans, Finnegan Lee Elder and Gabriel Christian Natale Hjorth, both 19, and from San Francisco, were able to escape briefly, but investigators tracked them to their luxury hotel room and managed to detain them as they were planning to leave the country, authorities said.

"The two, once in the barracks, were questioned by the Carabinieri, under the direction of the magistrates of the Public Prosecutor of Rome, faced with overwhelming evidence, they confessed," the Provincial Command of Rome said in a statement, translated from Italian.

An Italian Carabiniere, paramilitary policeman, patrols near the site where his colleague, Carabiniere Vice Brigadier Mario Cerciello Rega was stabbed to death by a thief in Rome, Friday, July 26, 2019.
Police said they searched the Americans' hotel room, and a knife "of considerable size" was found hidden in the ceiling along with the clothes believed to have been worn during the stabbing. Authorities said they captured the crimes on surveillance video.

A decree of detention has been issued for the U.S. citizens for aggravated murder and attempted extortion, the Carabinieiri said.

The two are being held at the Regina Coeli district jail in Rome.

The pair were allegedly trying to buy drugs just before the stabbing, but were sold a fake substance, a spokesman from the Carabinieri's press office told ABC News. Authorities believe the man they stole the bag from was not involved in the drug deal, but may have told the Americans where they could purchase drugs before he was robbed of his bag, the spokesman said.

A car of the Italian Carabinieri, paramilitary police, is parked near a blood stain, the site where Carabiniere Vice Brigadier Mario Cerciello Rega was stabbed to death by a thief in Rome, Friday, July 26, 2019.
Early reports by Italian media that the Americans went to John Cabot University are not true, a school spokesperson told ABC News.

Italian Deputy Prime Minister Matteo Salvini posted a photo of Rega from his wedding last June on his Twitter account.

Salvini had said before the official announcement of the teens' arrests and confessions that they would make the culprits "pay dearly," according to The Associated Press.