What the Josh Wolf case was really about

Here's what the Josh Wolf case was really about: A city cop, Peter Shields, was permanently injured during a juvenile political demonstration in the Mission:

Today's a good day for Shields: No pain. He gets headaches most days. Once in a while, they blossom into full-blown migraines, and he has to take the day off. The pain is a remnant of the time he got clocked in the skull during a protest against globalization. He spent a year on disability. (from last Sunday's Chronicle)

The question is, Why didn't the city's District Attorney go after whoever it was that injured Shields? 

District Attorney Kamala Harris isn't shy about sharing her opinions, as she recently wrote a guest editorial in the Bay Guardian that tries---and fails---to answer that question:

In San Francisco the US attorney has held journalist Josh Wolf in prison since September 2006. Wolf should be released...Of course, I believe crimes against police officers should be aggressively prosecuted. But I also believe that federal authorities have an obligation to respect the First Amendment. 

Free speech rights are critical to the work of journalists, university researchers, organized labor, and all of us in a democracy. The Justice Department should recognize the importance of protecting free speech, not only as constitutional and civil liberties issues but as smart public safety policy. Journalists play a key role in connecting us to individuals with information about crimes, and threatening the confidentiality of their sources has a chilling effect.

This sounds reasonable. But what about Peter Shields, who was seriously injured during the anarchist demonstration Wolf was filming? Harris tries to address the Shields problem, even though, interestingly, she can't bring herself to use his name in a guest editorial that panders to city progressives:

If sources fear their confidentiality will not be protected, they will be less likely to come forward to journalists with information that could expose corruption or assist us in solving violent crimes. Cities across the country are grappling with serious gang violence. 

Precious resources should be focused on addressing violence, gun crime, and major white-collar crime, not wasted on prosecuting journalists and conducting immigration raids that sweep up innocent residents, actions that hinder our efforts to build trusting relationships with vulnerable, victimized communities and keep the public safe.

But isn't fracturing a city cop's head a "violent crime"? Whether or not Wolf was/is a journalist, if he had evidence of who committed that crime, why didn't Harris even ask for it? 

Harris criticizes their immigration raids and arrests, but the Feds at least get credit for aggressively going after that evidence. 

City police are the community's first line of defense against crime. Surely trying to determine who committed an act of violence against one of them should be part of "keeping the public safe."