Authorities found a rifle with a scope, two semi-automatic handguns and a bulletproof vest inside that building in the 4600-block of North Broadway.
The standoff began with the arrest of one man in a firearms investigation. Three others surrendered late Monday night. One of them is now wanted in an Indiana murder case.
The situation forced the shutdown of part of the nearby CTA Red and Purple lines.
Charges against the four suspects have not yet been filed.