Finnish police said Janitskin, who is the founder of anti-immigrant magazine MV-lehti, is suspected of 46 offenses.
Janitskin was arrested in absentia in Finland, enabling police and prosecutors to obtain a European warrant for his arrest.
Finnish authorities want to speak with Janitskin on suspicion of inciting hatred against an ethnic group and aggravated slander and charges including money laundering and gambling crimes, illegal threats, breaches of confidentiality and copyright infringement.
He was reportedly arrested in Spain on Thursday but just a couple of days later on Saturday, Janitskin posted an update on Facebook that he had been freed.
Release in Spain puzzles Finnish police
On Monday Finnish Police Detective Harri Saaristola confirmed that Janitskin had been released but was unsure why.
"This is quite a surprise. Nothing like this has happened before during my career - that a person was arrested in another country and free again after a few days," Saaristola told Yle.
Janitskin's lawyer Matti Nurmela said that a Spanish court ruled his client could not be kept in jail. He said Janitskin is now allowed to move freely but was ordered to keep in regular contact with Spanish authorities.
The following step for Finnish law enforcement is to handle Janitskin's eventual extradition to Finland.
Saaristola told Yle that extradition requests between European countries are almost always granted.
Lawyer: Janitskin not guilty
Nurmela said that his client is not guilty of any of the allegations.
"He denies having committed any crime," Nummela said. "We oppose his extradition and the Finnish arrest warrant."
Nurmela said he proposes that Finnish authorities should come to interrogate Janitskin in Spain. He said that he does not know when the Spanish court will rule on the extradition request.
In Finland the police investigation of Janitskin continues. Saaristola said that it would not be complete until they speak with Janitskin personally.