A year that brought shocking killings in the Bay Area — including a quadruple slaying in central San Francisco and the random shooting of a woman on a pier 2 miles away — also saw overall homicides tick up nearly 10 percent, putting a crimp in a two-year downward trend that had heartened many police and community leaders.

The region’s 15 biggest cities recorded 243 killings last year, up from 222 in 2014, according to a Chronicle analysis. Despite the rise, violence in the Bay Area remains at relatively low levels historically, and the total represents a 33 percent drop from 2007.

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Robert Weisberg, a criminal justice expert at Stanford Law School, said the numbers — which do not include officer-involved homicides or killings police deemed driven by self-defense — appear to reflect national trends, but that criminal behavior “responds to a variety of factors and is one of the greatest mysteries in social science.”