Anti-terrorism officials told reporters on Friday that Mourad Sadaoui, 45, was the first foreign fighter to have gone from Italy to Syria and then be captured after returning to Italian soil.
Authorities said he was found in a farmhouse near Acerra, southern Italy.
Anti-terrorism official Claudio Galzerano told reporters that police are hoping cell phones found with Sadaoui will reveal how he managed to slip back in Italy, apparently undetected, in 2017 and then elude capture until now.
Sadaoui, sought by Algeria on a warrant for terrorism charges, had worked as a bricklayer in Italy for several years starting in 2003. Authorities said that in 2013 he traveled via Algeria to Syria.