Murder rate on the rise?

This story from USA Today is more than a month old, but it caught my attention because it is counter to the trend of lower violent crime rates which has been going on for more than two decades: 

"Several big U.S. Cities see homicide rates surge," said the newspaper's headline. Milwaukee, St. Louis, Baltimore, New Orleans, Chicago, Washington, D.C. and Dallas are reported to have jumps in their homicide counts. 

The homicide toll across the country — which reached a grim nadir in 1993 when more than 2,200 murders were counted in New York City — has declined in ebbs and flows for much of the last 20 years, noted Alfred Blumstein, a professor of urban systems and operations research at Carnegie Mellon University in Pittsburgh. Several U.S. cities – including Los Angeles, Phoenix, San Diego and Indianapolis – have experienced a decrease in the number of murders so far this year. Blumstein said the current surge in murders in some big cities could amount to no more than a blip. "It could be 2015 represents us hitting a plateau, and by the end of the year, nationally, we'll see that murder rates are flat or there is a slight bump up," Blumstein said.

No place seems to have it worse than Baltimore. The ABC TV station there last week reported that Charm City's murder rate is up 53 percent over 2014. 

Seventy more people have been killed in Baltimore this year compared to the same time last year.  Two more murders Monday pushed the city’s homicide rate to 201 deaths so far in 2015. It took until December to reach the same benchmark in 2014. At this time last year, 131 people were killed in the city.

I am not sure why this is happening, now. It's likely that part of the reason in some cities is a resurgent drug war, where gangs that had controlled some neighborhoods are being challenged by other gangs intruding on their turf. But if it proves to be a national trend over several years, gang turf instability won't explain much. 

EDIT: SEPTEMBER 2, 2015

Just noticed this story in today's LA Times: "L.A. homicides, after big jump in August, are up 7% for 2015." They seem to think much of the bump is due to gang violence:

Across the city, 185 people had been killed through Saturday. … Thirty-nine people were killed in L.A. last month, LAPD Chief Charlie Beck said, making it the deadliest August the city has seen since 2007, when 41 people were killed. … Nearly half of the 39 killings occurred in South L.A., Beck said. The chief attributed the majority of the violence to gang crime, which he said had also increased this year.