Police in Slovakia have released seven people detained in connection with the killing of a journalist, who was investigating the mafia, and his fiancée.

Their release came on the day mourners gathered to remember Jan Kuciak at his funeral and vowed to keep the spirit of his work alive.

The men were arrested on Thursday when police raided homes allegedly linked to members of an Italian crime syndicate.

The journalist and his partner Martina Kusnirova were found shot dead at home last Sunday. Mr Kuciak was working on a story revealing the influence of the Italian mafia in Slovakia and its alleged ties to people close to the Prime Minister, Robert Fico.

His article was published posthumously on the website he worked for, Aktuality.sk.

A police statement said the seven suspects, ranging in age from 26 to 62, were released because no evidence had emerged during the 48 hours they can be legally detained.

A funeral mass for Mr Kuciak was held at the church of St Francis of Assisi in the town of Stiavnik in western Slovakia. His parents, friends and fellow journalists packed the aisles.

Archbishop of Bratislava Stanislav Zvolensky, who led the funeral mass, said: “If the murderer wanted to silence Jan, he managed quite the opposite. There’s not a single person who wouldn’t know what happened.”

The archbishop added: “Evil won’t win, even if it might seem so now.”

Slovakia says farewell to Jan Kuciak at his funeral today (Getty)

On Friday, thousands of protesters braved icy weather to stage vigils across the country and abroad, including in London, Paris and Brussels.

In the Slovak capital Bratislava, among the 20,000 protesters, some carried photographs of Mr Kuciak and Ms Kusnirova, along with a banner reading: “An attack on journalists is an attack on all of us.”

The Slovak President, Andrej Kiska, joined the event where a minute’s silence was held.

An Italian former anti-mafia prosecutor has said Italian prosecutors warned Slovak authorities of “dangerous” infiltration into the country by a powerful Italian organised crime syndicate, the ‘Ndrangheta.

Franco Roberti told Italian radio: “We warned authorities in Bratislava, but unfortunately they didn’t heed us.”

Mr Roberti said the ‘Ndrangheta, based in southern Italy, might have killed the journalist and his fiancée because “there was no other way to silence him”.

Mr Fico has put up a million-euro (£900,000) reward for information leading to the conviction of the killer.