Editor's note: Peter Scheer, a lawyer and journalist, is executive director of the First Amendment Coalition, a nonprofit that advocates for freedom of speech and government transparency.
(CNN) -- Search warrants have always been a blunt instrument for finding evidence of crime.
Think of television cop shows from the '70s and '80s: A police search of an apartment for drugs was, de facto, a license to ransack all closets, cabinets and dressers. A warrant to seize a letter or other specific document was a green light to overturn desks and dig through all files and writings, no matter how personal.
But on a scale of intrusiveness, the threat to personal liberties posed by search warrants in the pre-digital era was trivial compared to the virtual strip-search that a warrant has become today.
This is illustrated by the ongoing investigation into Apple Computer's loss, and eventual recovery, of a supersecret prototype for the next-generation iPhone, which ended up in the hands of Gizmodo, a gadget blog, after the blog reportedly paid $5,000 to the person who found the missing phone.
Jason Chen, an editor-reporter for Gizmodo (which is owned by Gawker Media), returned home after dinner April 23 to find San Mateo County sheriff's deputies hauling away his computers, external hard drive, cell phones and digital camera -- all on the authority of a search warrant, requested by the San Mateo district attorney and approved by a Superior Court judge, for evidence of unspecified crimes related to the missing iPhone.
Imagine the disruption caused by this search and seizure of virtually every document, file and byte of data in Chen's possession, from e-mails to phone numbers to calendar entries and working files.
For you, me and most people, a loss of this magnitude would be crippling, essentially bringing one's work to a complete halt for the duration of a police examination in which government agents will have access, not only to business records, but also to one's most private files (medical and financial records, communications with family members, etc.). But for journalists, particularly investigative journalists, the loss would be catastrophic.
This is so because journalists obtain sensitive information -- about government, big corporations, other powerful institutions -- from inside sources who, for reasons good and bad, will disclose the information only if their role in releasing it is never revealed.
Journalists must be able to promise confidentiality to these sources. Equally important, journalists must be credible in these representations -- their sources must be persuaded that the journalists not only intend to keep their promise of confidentiality, but that they are able to keep it.
Use of search warrants against journalists is devastating because it demonstrates that they can't keep this crucial promise -- it is beyond their power. And the damage is not confined to the journalist who is the subject of a warrant, but extends, logically, to all reporters who have confidential sources.
In this sense the Apple iPhone case is not about Jason Chen and Gizmodo. Their ethical and legal calculations about paying a news source, or the importance of their "scoop" (relative to the harm to Apple's business), are beside the point. The iPhone investigators' use of a search warrant highlights a grave threat to independent journalism generally.
It didn't have to be this way. The DA could have, and should have, served Chen with a subpoena for records relating to the iPhone story. Use of a subpoena, unlike a warrant, gives the recipient an opportunity to hire a lawyer, to consider his options, and to assert any defenses or privileges that might be available.
Even if those arguments fail, and the reporter is ordered to produce records and information, the harms from a search conducted pursuant to a warrant -- including the jeopardy to journalists' access to confidential sources -- are avoided.
For these reasons, two laws, one federal and the other a California statute, require prosecutors' use of subpoenas, rather than warrants, to obtain information from journalists in criminal investigations.
Less clear, however, is whether this prohibition applies if Chen or Gizmodo are targets of the criminal probe, as some bloggers speculate they may be (although the DA has given no clues about their status, and criminal charges would seem to be a stretch under the circumstances).
The federal law, The Privacy Protection Act, may bar search warrants in this type of investigation even if the prosecutor is planning to charge journalists with crimes. That application, however, may be vulnerable to the constitutional argument that the privacy law exceeds federal power to dictate state judicial proceedings.
Perhaps there is a more mundane explanation for the failure to use a subpoena in this case: The DA may have been under intense pressure (from whom? Apple, which reported the phone was stolen?) to act even before he could convene a grand jury to issue a subpoena.
If so, the DA may come to regret his haste: If a court rules he shouldn't have used a warrant, the DA's possession of evidence seized from Chen's home may undermine any possible prosecution of other, more culpable, parties.
The opinions expressed in this commentary are solely those of Peter Scheer.