A doctor, a newly graduated pharmacist and a police officer were killed after a gunman opened fire at a hospital in Chicago, police say.

What happened?

What more do we know of the victims?

How big a problem is gun violence in America?

• In Philadelphia, Pennsylvania, the bodies of four people who had been shot dead "execution style" were discovered in a basement, US media report
• In Denver, Colorado, one person was killed and three others wounded. Police are still looking for the gunman