A man opened fire with a shotgun at a branch of Greece's EFKA social security agency, wounding an employee in the leg, police said.
The gunman then travelled by taxi to a court building, where he fired several shots inside, lightly wounding four female court clerks, according to police, court officials and the judiciary employees' union.
The gunman left the shotgun at the scene, along with letters addressed to newspapers, and fled on foot, media reported.
During the arrest, a second weapon was found, local media reported.
Media identified the suspect as a rubbish collector from the Athens area.
Police have not commented on a possible motive.
The man was arrested in a hotel in the western port city of Patras, 200km from Athens.
Witnesses described the man as confused, and police sources told the media he had received psychiatric treatment in recent years.
All the injured are out of danger, emergency services said.
Initial reports from broadcaster ERT indicated a dispute with authorities over pension payments may have triggered the incident.
with DPA
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