The New York Times has an interesting story on the police seizure of witnesses’ cell phones after the shooting of a knife-wielding man in Times Square on Saturday. I wrote about that issue a few weeks ago, and how the DC police department issued a first-of-its-kind policy on how officers should deal with evidence in citizens’ phones.

One of the innovative things about the DC policy is that it allows a citizen to email a relevant video or photograph to the police department. That provides a nice alternative to having the police seize the entire camera or phone and hold it as evidence for who knows how long.

The Times, however, quotes a legal expert as saying that police prefer to download data themselves out of fears that to do otherwise might raise questions about the chain of custody of the electronic evidence.

That seemed strange to me, since as we privacy advocates know all too well, electronic transmissions tend to leave behind very traceable trails—more so than offline transactions certainly. I asked my ACLU colleague Art Spitzer, who negotiated the DC policy as part of the settlement of an ACLU lawsuit, whether this chain of custody issue came up as they were hammering out that policy. Art told me:

Yes, it did. That's why the General Order says that a person whose smartphone has relevant photos or videos may, “in the presence of the member [meaning the police officer], voluntarily transmit the images or sound via text message or electronic mail to the member’s official government electronic mail account.” That way the officer can testify in court that she knows the images she received were transmitted from the camera that she didn't seize at the scene. The DC Metropolitan Police Department’s General Counsel and the DC Attorney General's office think this will provide an adequate chain of custody for legal purposes, and we think so too.

Clearly, maintaining a strong chain of custody is important both to protect the innocent from being falsely accused or convicted based on false evidence, and to enable prosecutors to convict the guilty based on good evidence. No doubt this procedure will be tested in the courts, where we hope it will be upheld, so that individuals can avoid having their phones seized, and be less subject to invasions of privacy by police officers who might be tempted to peruse the other contents of their device (which, as I discussed in my prior post, the DC policy prohibits, in addition to requiring a warrant to access any data on a device that is not voluntarily shared).