Why did violence break out at the demonstration of haymarket riot?

The workers at Haymarket Square strike to protest for higher wages. But, the owners didn't really care, they just hired new workers that replace the old ones. When they met, there's was conflict happening. After the police arrived, they killed 4 workers. The next day the workers (new and old) gather to protest the killing, a bomb is thrown at a squad of policemen attempting to break up what had begun as a peaceful labor rally. The police responded with wild gunfire, 7 police officers died.