Serbia's striking university students on Wednesday rallied outside the chief prosecutor's office to demand justice over a concrete canopy collapse that killed 15 people last month in the country's north.

More than 1,000 students symbolically left letters on the doorstep of the public prosecutor's office, telling chief prosecutor Zagorka Dolovac that "students expect you to fight for law and justice, without political abuse or corruption.”

Dolovac's office later responded with a statement inviting a student delegation to a meeting.

Serbia's universities have been blockaded for weeks as part of a wider movement demanding accountability over the Nov. 1 tragedy in Novi Sad when a huge concrete construction at the railway station crashed onto the people below.

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Many in Serbia blame the collapse on widespread corruption and sloppy work on the building renovation, one of a number of questionable infrastructure megaprojects involving Chinese state companies.

Prosecutors have arrested 13 people over the Novi Sad tragedy, including a government minister whose release later fueled public skepticism about the honesty of the investigation.

Striking students have received wide support in Serbia from their professors, farmers, actors and others. Tens of thousands joined a student-led protest in Belgrade on Sunday that also reflected wider discontent with populist President Aleksandar Vucic's rule.

Protesting students on Wednesday carried banners featuring red handprints — a protest symbol telling the authorities they have “blood on their hands.”

In an apparent attempt to defuse the student strikes, Vucic has been advertising what he describes as “favorable” loans for young people to purchase apartments.

The increasingly autocratic Serbian leader has faced accusations of curbing democratic freedoms despite formally pursuing European Union membership for the Balkan nation.