On Tuesday, the San Francisco Chronicle reported that local officials, in collaboration with investigators from the Federal Communications Commission, have now found the culprit in the Oakland Police Department’s ongoing public safety radio woes: AT&T.

Last week, FCC and the City of Oakland notified the mobile network that its towers were interfering with the radios, but the problem got significantly worse when a police car found itself within a quarter-mile of a tower. (That is, according to David Cruise, the city’s newly hired public safety systems adviser, as reported by the Chronicle).

"If the officer is in an area close to one of their cell sites, essentially the cell site overpowers their radios," he told the paper.

Neither the Oakland Police Department, nor the FCC, nor David Cruise responded to our request for comment.

A failing $18 million investment

Since July 2011, the Oakland Police Department has been using a new $18 million police radio system that has suffered numerous failures—one major occasion was as recently as last month, just after President Barack Obama departed town for a fundraiser.

Police and local officials have been scratching their heads trying to figure out what’s gone wrong. The Bay Area city, home to 400,000 residents, has had problems with its understaffed police force over the last year (remember Occupy Oakland?). A basic issue like radio communications certainly doesn’t help things.

In late July, one local columnist thundered: "It's time for city officials to bite the bullet, eat the cash loss, and invest in a reliable, inter-modal radio system before someone gets hurt—or killed."

Worse still, Oakland boasts the largest population in the East Bay region and has declined to join a network of 40 police and fire departments that are working on building a unified public safety radio network. So for now, the radios also don’t work in hundreds of buildings around the city, including the downtown basement of the Oakland Police headquarters.

AT&T shuts down 2G frequencies

As a result, AT&T shut down its 850MHz (2G) frequency on 16 cell sites around the city, which it has used for nearly two decades in the city.

"AT&T is working closely with the City of Oakland to understand if the issues they’ve raised are connected in any way to AT&T’s network," wrote Seth Bloom, a company spokesperson, in an e-mail sent to Ars.

"In the interest of public safety and as a cautionary measure while we’re looking into the matter, we have temporarily taken some 2G frequencies out of service at some cell sites in Oakland. We continue to operate on other 2G frequencies and our 3G and 4G service throughout the area is unaffected."

Many mobile phone networks can cause interference with existing public safety networks, which take priority. That’s why some networks pay to "re-band" their networks to frequencies farther away from public safety ones, which is what Sprint Nextel did in 2011—paying $10.5 million for the privilege.

Cruise also told the Chronicle that while the two companies involved in installing Oakland’s new radio system, Daily Wells Communications Inc. and Harris Corporation, checked for interference, they may not have done a thorough job. Those two vendors also did not respond to requests for comment.

"Unless they drove close to a cell site, they wouldn't have seen this," Cruise said.