Grieving family, colleagues and friends filled a church in Somma Vesuviana, the hometown of officer Mario Cerciello Rega, 35, who suffered multiple knife wounds on Friday in an attack that the suspects claim was in response to a drug deal gone wrong.

Two Americans, Gabriel Natale Hjorth, 18, and Finnegan Elder, 19, have been charged with aggravated homicide and attempted extortion following the murder in Rome’s upmarket Prati neighbourhood.

Crowds applauded as the hearse bearing Cerciello Rega’s coffin arrived at the church near Naples, which is the same church he had been married in six weeks earlier.

The casket, draped in the Italian flag, was carried by police pallbearers into the church as a military trumpet rang out.

Deputy Prime Ministers Matteo Salvini and Luigi Di Maio were among the government officials attending the funeral.

A photograph of Cerciello Rega and his wife Rosa were placed on the coffin, along with an AC Napoli football shirt.

The murdered officer had recently returned home from his honeymoon.

He was stabbed 11 times with a bayonet knife with an 18-centimetre blade, local media reported.

According to police, the suspects said they did not realise that Cerciello Rega and his colleague were police officers.

They claimed they believed the officers were friends of an alleged drug dealer from whom the pair had stolen a bag which was supposed to contain cocaine but turned out to be crushed aspirin, according to media reports citing investigators.

The victim of the theft tipped off the police, but when two officers in plain clothes went to arrest the two American tourists, one of them allegedly pulled out a knife.

“We have remembered Mario in tears: all the lovely things, the moments spent together,” the mayor of Somma Vesuviana, Salvatore Di Sarno, told reporters.  

“But also the tragedy – a terrible affair which cannot go unpunished.”

The US embassy to Italy tweeted its condolences and said it shared “the grief of [Cerciello Rega’s] family and the police”.

The funeral comes amid controversy over a picture of the suspects blindfolded and handcuffed while being questioned by police. 

The suspects are being held at Rome’s Regina Coeli prison.

Neither of them “have shown they have understood the seriousness of the consequences of their behaviour”, Rome judge Chiara Gallo said in her order for the pair to be remanded in custody.

She said the teenagers from California showed “total absence of self-control” and “an immaturity excessive even for their young age”, making them highly dangerous to society.

Police said surveillance cameras helped them track down the suspects to their four-star hotel where they were arrested hours after the attack.

Their bags were packed and they had been planning to fly home the same evening.

Officers allegedly found a large military-style knife hidden in the hotel room’s drop ceiling.

Italy’s military chaplain, Archbishop Santo Marciano, said in his eulogy that Cerciello Rega lived and died to safeguard others’ lives, adding that the officer was known for spending his off-duty hours as a volunteer dishing out hot meals to the homeless in Rome’s main police station.