By Nick Thorpe
BBC News, Budapest
The suspects were arrested at a nightclub
Hungarian police say they have detained four men suspected of a series of attacks on Roma (Gypsy) settlements in which six people have been killed.
The attacks have sown terror among the Roma, who make up around 7% of the Hungarian population.
The men - aged 28 to 42 - were arrested at a nightclub in the eastern city of Debrecen in the early hours of Friday.
Evidence found at their homes and the crime scenes linked them to the killings, police said in Budapest.
The national police chief, Lt Gen Jozsef Bencze described the attacks as the "biggest, most complicated and most serious series of murders" in Hungarian history.
Hungarian President Laszlo Solyom said the whole country can now breathe a sigh of relief.
Pattern of killings
The most recent murder of 45-year-old Maria Balogh took place only 18 days ago.
The attacks - carried out with shotguns, hand grenades and homemade explosives - began in July last year.
Police soon identified a pattern.
The victims invariably lived among the last and most exposed houses in the rural ghettoes in which most Hungarian Roma live.
In each case, there was also a motorway nearby, facilitating a quick escape.
A 100-member taskforce has been trying to track the perpetrators, and a large reward has been offered.