The prosecutor had sought to have the men sentenced to three years in prison, but the Gothenburg District Court ordered the three men released from custody following the conclusion of the trial in December.
“As they were released following the hearing, it wasn't unexpected that the main charges were thrown out,” prosecutor Agnetha Hilding Qvarnström told TT on Friday after the verdict was announced.
However, she added that she had no regrets about filing charges against the men.
“They were held in remand for a long time and they ordered held in remand on several occasions. The matter was tested in court and I believe there was reason to indict them,” she said.
Vilks has faced numerous death threats and was the target of another suspected assassination plot since his drawing of the Prophet Muhammad as a dog was first published by a Swedish regional newspaper in 2007, illustrating an editorial on the importance of freedom of expression.
The three men released Wednesday were arrested along with a fourth man, no longer considered a suspect, by an elite counter-terrorism unit in Gothenburg.
The unit had evacuated hundreds of people from the Röda Sten gallery that was hosting the September art fair "after concluding that there was a threat that could endanger lives or health or cause serious damage".
Vilks had initially said on his blog that he would attend the art fair although he did not in the end.
The three suspects -- one Somali citizen and two Swedes in their mid-20s – were all carrying knives when they were arrested and were, according to the prosecution, planning to stab Vilks to death.
Press reports have suggested that the trio had ties to a Somali Islamist movement al-Shabaab, but Hilding Qvarnström told AFP in December that she had no information to support such claims.
She said she has yet to decide whether or not she will appeal the ruling.
“I now want to read the verdict and the court's reasoning in peace and quiet. I have three weeks to decide,” she told TT.