The Russian citizens, Maxim Zhurkin, Sergei Solovey and Dmitry Gafarov, are charged with terrorism, while the Latvian, Vladimir Moskovtsev, is charged with assisting them.
Prosecutors say the three threatened to blow up the tower with a hand grenade, even though it later turned out to be fake. If found guilty of terrorism the defendants face between 15 and 20 years' imprisonment, a response that Leonid Raihman, a minority rights advocate, said would be an overreaction.
"I'm convinced there is too much noise surrounding this trial," said Raihman. "They caused no danger or real damage. Shouldn't they be charged with a lesser offense?"
The National Bolshevik movement, which is based in Russia and is known there by its logo of a hand-grenade, uses unorthadox means to campaign, among other things, against NATO membership in former Soviet countries.
The trial, which resumes again on April 20, continues to attract a small crowd of spectators, including members of the National Bolsheviks' Latvian wing, sporting hammer and sickle badges, and an older lady who was thwarted by police in her efforts to give bluebells to the "children" in the dock. Gafarov is under 18 years of age. He is classed as a juvenile under Latvian law.
At the end of April 17's hearing their lawyer, Sergei Belyak, was rumored to have returned to Russia in order to visit National Bolshevik leader Eduard Limonov, who has been arrested on arms purchasing charges in the Altai region of western Russia, according to Russian media reports.
Attitudes in Latvia toward the defendants could harden in response to the latest developments in Russia, said Nils Muiznieks, director for the Center for Human Right and Ethnic Studies. An unknown number of National Bolsheviks were arrested for attempting to acquire large quantities of firearms, ammunition and explosives, according to the Russian media.
If, as many predict, the defendants are found guilty and extradited to Russia, their treatment by the authorities may be harsher than previously expected.
"Lomonov's arrest makes these guys look more ominous," said Muiznieks.
"My impression was that the National Bolsheviks were playing at revolution, but not actually carrying out acts of terror, but this indicates that the movement is evolving in a new direction. The Russian authorities have until now turned a blind eye to the National Bolsheviks, but their recent actions suggest they are taking a harder line."
On April 11 Latvia's embassy in Ukraine submitted a note to Ukraine's Foreign Ministry requesting better protection of its buildings after a number of incidents which have been connected to the National Bolshevik organization there. The embassy building in Kiev was daubed with paint on the night of April 10.
The next day around 20 members of the group gathered in front of the building and burned an effigy of Latvian President Vaira Vike-Freiberga, according to the Baltic News Service.
At the opening of the trial on April 10, Gafarov admitted he had entered Latvia illegally, but denied the other charges. The other defendants denied all charges and claimed they had been beaten by police while in custody. Didzis Smitins, deputy chief of the security police told the court the defendants' complaints were untrue.
Russian-language media in Riga expect the trial to conclude on April 23.