Gavrilo Princip wrote a poem in his prison cell. There is a link in Serbian.

Below is my impromptu translation of the poem

Sarajevo 1914

Slowly the time is dragging

And there is nothing new

Today is same as yesterday

Tomorrow will be too.

And instead in war

While battle trumpets are crying

Here we are in a casamate

Chains on us are rattling.

Every day is the same life

Trampled, stomped, crushed

I am not an idiot

This is death for me.

The truth said Žerajić before me

Who wants to leave let him die

Who want to die let him live.

It looks like a similar question was asked before. It would be nice to see some more info or verification of those answers, but hopefully that's a good starting point.