California shooting marks 20-year low in US mass killings – but the bigger picture is complex

Experts warn the drop doesn’t necessarily mean safer days are here to stay – and US deaths from firearms are still staggering

A shooting last weekend at a children’s birthday party in California that left four dead was the 17th mass killing in the US this year – the lowest number recorded since 2006, according to a database that tracks them.

The mass killings – defined as incidents in which four or more people are killed in a 24-hour period, not including the killer – are tracked in a database maintained by the Associated Press and USA Today in partnership with Northeastern University.