Why number of US mass shootings has risen sharply

California has woken up to news of three mass shootings this week. On Monday, a gunman opened fire at two plant nurseries in Half Moon Bay, killing seven and injuring one person.

A few hours later, another gunman opened fire 41 miles (65km) away at a petrol station in Oakland, injuring seven and killing one person.

Then on Saturday, 11 people who had gathered to dance died on the eve of Lunar New Year in Monterey Park near Los Angeles.

If it feels like these incidents are becoming more frequent...