The 29-year-old man, whose name was not reported, was detained about a week ago in Ostrava, the BBC reported Saturday. Police have just released information about what they found in the suspect's apartment, including an assault rifle, explosives, ammunition and police clothing.
The man was planning to detonate a large explosive device crafted from an aircraft bomb and was in possession of a remote control detonator when he was arrested, the BBC said.
Police said they do not know the suspect's intended target but verified his weapons were all functional. Authorities were alerted to his plan because he used the name Breivik in e-mail correspondences, the BBC reported.
The real Breivik is on trial for killing 77 people -- eight in the bombing at a government building in Oslo and 69 others on nearby Utoya Island -- July, 22, 2011.
Breivik, who admitted to the killings but said they were justified, is on trial on homicide and terror charges and a verdict is expected next week. He claimed "self-defense" and said his actions were justified because he was waging war against multiculturalism and what he termed was a Muslim invasion of Europe.