The intercepted call had been recorded by an automatic-taping system and stored on a server accessible to prosecutors, who downloaded the conversation and shared it with McMahon.
"We weren't talking about cursory stuff, what kind of clothes to wear. We were talking trial strategy," McMahon said. "There's no question that these calls are privileged, and we rely on that because the criminal justice system would come to a screeching halt if we had to drive to the jail every time we had to talk to our clients."
After McMahon's call came to light, San Diego authorities briefly shut down the recording system last month to add safeguards. But thousands of jails and prisons nationwide use similar automatic-recording systems to monitor inmate calls, raising questions about the privacy of attorney-client conversations.
Discussions between attorneys and their clients are among the most highly protected communications in the legal system, and breaching their confidentiality is considered a serious violation of inmates' constitutional rights.
In California, it's a felony for anyone to eavesdrop without permission on inmates' phone calls with attorneys, doctors, psychologists and clergy. But that has not prevented problems. In the past two years, privileged conversations between inmates and lawyers have been recorded in Alameda, Santa Clara and Riverside counties in California, as well as Broward County, Fla.; Lansing, Mich.; and Dallas.
The breaches typically come to light during preparation for trial, when prosecutors are required to share evidence with defense lawyers.
Jail systems have long recorded inmate calls to watch for illegal behavior or investigate crimes. But before automated systems were introduced two decades ago, deputies could switch off the tape if an inmate called a lawyer.
Newer digital systems automatically turn off the recorder if an inmate dials a number included in a database compiled by authorities, who typically rely on directories published by local bar associations to identify lawyers. That means calls may be improperly recorded if the databases are incomplete or out-of-date. San Diego County sheriff's officials said they don't know how many privileged calls were recorded, but at least two lawyers besides McMahon have told courts they have evidence their calls to clients were taped.
In 2006, the U.S. attorney's office in San Francisco dropped gun-possession charges against a man after a prosecutor acknowledged listening to just 35 seconds of a recorded call the defendant placed to his attorney from a jail in Oakland.
In Broward County, Fla., the sheriff's department recently settled a class-action lawsuit filed after at least two inmates found their protected calls were inadvertently uploaded during a two-week test of a new $18 million recording system in 2006.
Authorities argue that attorneys and inmates have always been cautioned that calls to and from jail may be monitored. In San Diego, recorded warnings were played before every call, but some defense attorneys complained that wasn't enough.
The sheriff's department relied on public attorney directories when it switched phone-system vendors in February 2007 and made little effort to solicit additional mobile or home phone numbers from lawyers; to account for lawyers coming from other areas; or to protect other kinds of privileged calls, such as those to doctors or religious advisers.
"Anyone could call and ask that their numbers be added to the database, but the problem was that we didn't do as much as we could have in publicizing this fact," county legal adviser Sanford Toyen said in an e-mail. Toyen added that no effort had been made to include doctors or clergy in the database.
The recording system reactivated in early July now broadcasts a special number before each call for anyone who wants to apply for an exemption along with repeated warnings that calls may be recorded.
San Diego prosecutors have filed affidavits swearing that they had no idea the calls were taped. But defense lawyers say they should not have to rely on the integrity of government lawyers to protect their clients from potential harm.
To prevent improper recordings, Riverside County in California provided lawyers with codes to prevent their calls from being recorded. In Los Angeles, public defenders have access to a videoconference that can't be taped.
Los Angeles-based Public Communications Services Corp. runs phone systems in more than 100 state and federal prisons and jails across the country, including San Diego County. Dallas-based Securus Technologies Inc. serves 3,100 correctional facilities in 49 states.
"The first thing you hear when you pick up the phone is that your call can be recorded," said Rudy Zaragoza, a spokesman for Public Communications Services. "If you didn't register your phone number with the list, then you didn't do your job. The onus is on you."