BRATISLAVA, Slovakia — The police in Slovakia arrested eight people on Thursday suspected of being connected to the killing of a young investigative journalist and his fiancée seven months ago, a grisly crime that shocked the Central European nation and spurred large-scale demonstrations that ultimately forced the prime minister to resign.

The journalist, Jan Kuciak, 27, was investigating links between top government officials and people suspected of links to organized crime, when he and his fiancée, Martina Kusnirova, also 27, were shot dead in their home in February.

In an early-morning raid in Kolarovo, a small town in southern Slovakia, the police arrested eight people, including one man the authorities said might have been a paid hit man who carried out the killings.

The authorities declined to release the names of those detained or to provide details about why they believed one might have been the killer, saying that the investigation was continuing and that they did not want to do anything to compromise it.