One of them involved an off-duty Chicago police officer on the city's South Side.
Police say the officer saw two people exchanging gunfire near 127th and South Parnell. When the officer identified himself, one of the shooters pointed his weapon at the officer.
In fear of his life, the officer opened fire.
The gunman fled the scene.
A man later turned up at Roseland Community Hospital with a gunshot wound.
He is now in police custody.
The Independent Police Review Authority is investigating the situation.