BELLINZONA, Switzerland — Prosecutors in Switzerland's highest criminal court Wednesday recommended prison sentences of at least three years for a trio of alleged eco-terrorists charged with plotting a bomb attack on a planned IBM nanotech research facility near Zurich.

Federal prosecutor Hansjoerg Stalder said the three brought powerful explosives to Switzerland in the spring of 2010 to carry out their intended attack on IBM's $90 million research center, which opened in May.

"They came as criminal tourists to Switzerland," Stadler told the court.

The trial, held under tight security in the Federal Criminal Court, has drawn attention to a loose network of European anarchists who have grown more violent and coordinated during the continent's financial crisis and been linked to recent bombings in Greece, Switzerland and Italy.

Police said the three defendants — 35-year-old Costantino Alfonso Ragusa, his 29-year-old wife Silvia Ragusa Guerini and their 26-year-old Swiss friend Luca "Billy" Cristos Bernasconi — were arrested last year carrying explosive gel and several types of fuel — a combination with almost the explosive power of TNT.

But the defense argued that police wrongly treated the three as presumed criminals from the start, snaring them in a fake traffic stop near Zurich, about two miles (3 kilometers) from the IBM facility.

Stalder described the defendants, the Italian couple and a Swiss man, as having close links to the Earth Liberation Front (ELF) and Animal Liberation Front (ALF), both extremist movements that have claimed responsibility since the 1990s for a variety of what authorities describe as eco-terrorist attacks in Europe and the United States.

He said Ragusa and Guerini are known as founders and members of the Italian movement "Terra selvaggia," or Wilderness, which has connections to ELF, and that Bernasconi is an Italian member of ALF.

Stalder said each of the three should serve at least three years in prison, without suspending any of the time already served since their arrests, because of the seriousness of the planned crime.

A verdict is expected Friday.