By LIZETTE ALVAREZ
MIAMI — When Mark O’Mara agreed to defend George Zimmerman in the Trayvon Martin murder case, one of his first major decisions was to embrace the Internet.
He set up a legal defense Web site for his client, a Twitter page and a Facebook account, all with the purpose of countering what he called the “avalanche of misinformation” about the case and Mr. Zimmerman.
It was a risky move, unorthodox for a criminal defense lawyer, legal experts said, but a bold one. Late last month, the judge in the case, rebuffing the prosecution, allowed Mr. O’Mara to keep the online presence.
In so doing, the judge sanctioned the use of social media in a high-profile murder case that was already steeped in the power of Facebook, Twitter and blogs. Not long after Mr. Martin was shot and killed, protesters took their cues from Facebook and demonstrated across the country. Angry words coursed through Twitter.
Mr. Zimmerman, in hiding, started a Web site to raise money. The Martin family’s lawyers, who made ample use of traditional media, used Twitter to bring attention to Mr. Martin’s death.
Social media is playing a role in the courtroom, too. Mr. O’Mara wants to use Mr. Martin’s Facebook page and Twitter feed to bolster Mr. Zimmerman’s claim of self-defense. But he will most likely face a protracted battle to authenticate the material, in part because Mr. Martin is no longer alive. Last month, the judge allowed Mr. O’Mara to subpoena Twitter and Facebook for the information.
In ways large and small, the State of Florida v. George Zimmerman is serving as a modernized blueprint for deploying social media in a murder case.
“The way the whole case has been playing out in social media is typical of our times, but more typical of civil cases than criminal cases,” said Robert Ambrogi, a lawyer and technology expert who writes a blog on the intersection of the legal profession and social media. “It’s not without precedent, but it’s on the cutting edge.”
In civil cases, lawyers routinely dig up Facebook photos of people claiming to have a back injury dancing atop bars or revealing posts from supposedly faithful spouses.
“In the world of electronic information, the amount of potentially relevant information in discovery has exploded,” said Kenneth Withers, the director of judicial education and content for The Sedona Conference, a nonprofit law and policy research organization, referring to the pretrial exchange of information and evidence between lawyers on both sides. “And with social media, there has been an explosion of an explosion.”
It no longer makes sense for criminal defense lawyers who have tread more cautiously into social media to brush it off or avoid it, legal experts said.
Nicole Black, a co-author of “Social Media for Lawyers,” said criminal lawyers are getting crash courses on how to best use social media to help their clients and themselves.
“There is almost hysteria among the lawyers to understand it and how it’s affecting their practice,” said Ms. Black, who is also the director of business development and community relations at MyCaseInc.com.
Mr. O’Mara said as much in court recently when he pressed for access to Mr. Martin’s Facebook page and for the continued use of the legal defense Web site and its Twitter feed. “This is 2012, and I’m sorry, I used to have the books on the shelf, and those days are long gone,” he said. “We now have an active vehicle for information. I will tell you that today, if every defense attorney is not searching for information on something like this, he will be committing malpractice.”
Mr. Zimmerman, a Hispanic neighborhood watch volunteer in Sanford, Fla., is charged with second-degree murder in the shooting death of Mr. Martin, an unarmed black teenager who was killed in February as he walked to a house where he was staying as a guest.
Mr. O’Mara has been careful to hew to ethical requirements on his Twitter feed and Web site, which he uses to post legal documents, react to developments in the case and raise money for his client. He allows comments to be posted so long as they are not inflammatory. When the Facebook page “devolved into people bickering,” he said, he shut it down.
Social media is difficult to control, which for many is precisely its allure. Last month, Mr. Zimmerman’s brother, Robert Zimmerman Jr., fired off an angry post on Twitter at Natalie Jackson, one of the Martin family’s lawyers.
“My Life’s work = you WILL be held accountable for your words/actions. You A’INT seen NOTHIN’ yet ... I will see U disbarred,” he posted on Twitter.
Mr. O’Mara wrote a reaction on his Web site.
“Regarding Robert Zimmerman Jr.’s media campaign and Twitter comments, Robert is acting on behalf of his family, and he is not acting with the approval or the input of the defense team,” he wrote. He noted that, “The Zimmerman family has been through a lot, and they have been frequently misrepresented in the media, so we do not begrudge Robert for wanting to speak out and set the record straight.”
While Mr. O’Mara has become adept at social media, rattling off the number of Google hits on the words Trayvon Martin and the tally of visits to the legal defense site — 267,089 as of Monday — plunging into the world of Twitter, Facebook and blogs is not a welcome development for all in the courtroom.
“I’m new to this, quite frankly; I’m old,” a prosecutor, Bernie de la Rionda, said as the two sides faced off over social media in the courtroom.
Before long, Judge Debra S. Nelson will have to decide how to handle social media during the trial, which is scheduled to begin on June 10. Some jurors in other cases across the country have taken to posting about the proceedings on Facebook or Twitter, posing a risk of mistrials. Judges have cracked down.
Considering the publicity in the case, Judge Nelson may wind up following the lead of the judge in another high-profile Florida murder trial, that of Casey Anthony, who was acquitted of killing her young daughter. She could sequester the jury members, confiscate their cellphones and laptops, and monitor their calls and computer time.
If Judge Nelson does follow suit, she must be prepared to deal with another juror dilemma: extreme withdrawal.
A version of this article appeared in print on November 7, 2012, on page A16 of the New York edition with the headline: Social Media, Growing in Legal Circles, Find a Role in Florida Murder Case.