The trial was rife with evidence and witness tampering, a packed jury, and even the prosecuting attorney was caught admitting in private the innocence of the accused. But that didn't matter. Their real crime was of being anarchists and labor agitators who were threatening the profits of Chicago's elite.
For more information, see http://dwardmac.pitzer.edu/anarchist_archives/haymarket/Haymarket.html .
Remember the veterans of the class war!