ORLANDO, Florida (AP) -- It started a couple of weeks ago with a few cryptic messages on Twitter and other social media websites: Where is the justice? and R.I.P. TrayvonMartin.
A day later, nationally syndicated radio host Michael Baisden sent out a message to his 65,000 Twitter followers and 585,000 Facebook fans, adding a few details.
"Unarmed 17-year-old boy shot by neighborhood watch captain in Sanford, FL outside of Orlando," the tweet said. It provided a web link to a story.
Since then, hundreds of thousands of messages have spread the word about Trayvon Martin, a black teenager who was shot to death Feb. 26 by neighborhood watch volunteer George Zimmerman. Racial tensions have rapidly escalated as civil rights groups have held rallies, saying the shooting was unjustified.
President Barack Obama even commented on the case Friday, responding to a question about it by calling the case a "tragedy" and saying "every aspect" of it should be investigated.
Martin's parents started an online petition on Change.org demanding Zimmerman's arrest. It has had more than 1.2 million signatures.
Zimmerman claims self-defense, saying he shot Martin after being attacked by him. Zimmerman's father is white, and his mother is Hispanic.
Filmmakers Michael Moore and Spike Lee have also posted messages in support of Martin.
Martin, who lived in Miami, was in Sanford visiting family when he went to a convenience store. He was walking back carrying a bag of candy and can of iced tea, the hood of his jacket pulled over his head because it was raining. He was approached by Zimmerman, who told a police dispatcher he thought Martin looked suspicious. Zimmerman shot Martin following a chase and fight.
The online uproar grew after the first emergency call tapes from the day of the shooting were released last week. In one of the calls, a dispatcher told Zimmerman to stop following Martin, but he continued.
Twitter messages about Martin have been mentioned almost 600,000 times, according to the social media monitoring firm PeopleBrowsr. On Facebook, some protesters are wearing hoodies in their profile photos with the caption, "Do I look suspicious?"
The Justice Department and FBI have opened a civil rights investigation, and the local prosecutor has convened a grand jury April 10 to determine whether to charge Zimmerman.
"What you're seeing is that the Trayvon Martin case speaks to people around the country just like it speaks to people in this community," said Benjamin Jealous, president and CEO of the National Association for the Advancement of Colored People. "It would have been easy for people here to say, 'He wasn't one of us. I didn't know him. My kids didn't go to school with him.' But instead, people here are saying what people said around the world, which is, 'He reminds me of my cousin, of my son, or my grandson.'"
Not all the online sentiments side with the Martin point of view.
Kyle Rogers blogs at Examiner.com and is also a national board member of the Council of Conservative Citizens. He wrote a post for Examiner asking questions about the facts that have been reported in mainstream media to this point.
The post has gotten more than 12,000 Facebook shares.
"Almost all news items are written solely from the point of view of the grieving family," Rogers wrote. "The media also fills their articles with outdated baby-faced pictures of Trayvon. Very few include that he was a towering 6'2" football player. Is the media really reporting the news, or is this classic agitation/propaganda to advance a political agenda?"
Contacted by The Associated Press, Rogers defended his position further.
"It is much more than a rush to judgment," he wrote in an e-mail to the AP. "The media has intentionally hammered a grossly distorted version of what happened to advance a political agenda."
Jeanette Castillo, an assistant professor of digital media at Florida State University, is tracking the Martin case on Twitter.
She said the case has played out in a protest era that will be increasingly driven by online audiences.
"You can hear about an issue in traditional media and be outraged. But in social media you have immediate feedback of how much your friends are outraged," Castillo said. "It's just a huge facet of social media that affects that mobilization. It's sort of the same thing as word of mouth, but just at a lightning speed."
Recent research by the Pew Research Center's Internet & American Life Project shows why this case might particularly resonate for the black Internet audience.
Aaron Smith, a senior researcher for Pew Internet, said a study updated last month shows that 15 percent of all Internet users nationally use Twitter, including 8 percent on a typical day.
White users are generally in line with the national average with 12 percent using the service or 7 percent on a typical day.
By contrast, black Internet users have very high rates of Twitter usage, with more than a quarter using Twitter overall and 13 percent using Twitter on a typical day.
"It's a bit different data than we've seen historically," Smith said. "For a long time, it was always a digital divide story. But with social (media) we're finding the black community on par with or ahead of their white counterparts with usage."
Associated Press writer Suzette Laboy in Sanford contributed to this report.