Police in Albertslund released a 16-year-old suspect in the case, The Copenhagen Post reported Thursday.
"We are maintaining our charges against him and we are continuing to investigate the case," Michael Storgaard, the chief investigator in the case, told the Ekstra Bladet newspaper.
Another suspect -- an 18-year-old man -- is still in police custody, The Copenhagen Post said. He was arrested shortly after a March 12 fire at a community center in the city. He was released but then arrested again later.
The 16-year-old suspect was arrested a few days after the community center fire.
Since Sept. 12, 2012, there have been 103 arson cases in Albertslund. Structures that have been set ablaze include storage containers, cars and sheds.
Residents of Albertslund have started a Facebook group called "Stop the fires in Albertslund," which has almost 700 members.