Change.org, the online campaigning tool whose petition on Trayvon Martin has attracted more than 2m signatures, has predicted that there will be another massive surge in public anger against authorities in Florida if no charges are brought against the teenager's killer.
Staff at the petitioning website, which played a key role in propelling the Trayvon Martin story onto the national and international stage, are focusing on the convening of a grand jury on 10 April as the next crucial moment.
Jurors will be presented with evidence gathered in the killing on 26 February of Martin, an unarmed 17-year-old black boy, by George Zimmerman, a self-appointed "neighbourhood watch leader" in Sanford, Florida.
The grand jury will then decide whether or not to press charges.
Ben Wikler, change.org's campaigns chief, predicted the outcome of the grand jury would have far-reaching consequences. "The petition is directed at Florida officials, calling on them to prosecute Zimmerman for the killing of Trayvon. If they decide not to, they should expect a huge reaction in the US and worldwide."
The warning is no idle threat: the power behind the petition has already been demonstrated. Initiated by Trayvon's parents, Tracy Martin and Sybrina Fulton, it provides a dramatic illustration of the ability of social media to galvanise a cause.
It also illustrates the potential force of change.org itself, an organisation set up just five years ago that has more than 10 million members. The website exists to empower people to start their own campaigns on any issue they care about, acting as a platform upon which more than 15,000 new petitions are launched every month.
The total number of campaigns launched under the aegis of change.org has this week surpassed 100,000.
Even as seasoned an observer of social media, as Wikler says, he has been taken aback by the pace and scale of the Martin campaign. The website has put out a graph showing the trajectory of the petition superimposed against the main events in the investigation into the teenager's killing.
For 10 days after Martin's death very little happened. Then on 8 March, encouraged by their lawyer, Martin's parents posted the petition on change.org.
It reads: "Please join us in calling on Angela Corey, Florida's 4th District State's Attorney, to investigate my son's murder and prosecute George Zimmerman for the shooting and killing of Trayvon Martin."
For another five days the silence continued – a quite normal response, Wikler says, because it takes a while for most petitions to take hold. But then on 13 March it started to build, and the following day received a big boost with the signing up of celebrities such as Spike Lee and Mia Farrow. Numerous other public figures followed suit over ensuing days, from Cher and MC Hammer, to President Obama who made the memorable observation that "if I had a son he'd look like Trayvon".
From that point it took on a life of its own, going viral as it was shared on social media. So far it has been shared by 175,000 people on Facebook, emailed 70,000 times and featured in 20,000 tweets.
As noise surrounding the petition grew, the authorities became more proactive. A day after the change.org petition reached 300,000, the FBI and department of justice announced investigations. Three days after that, on 22 March, Sanford's police chief, Bill Lee, who had refused to arrest Zimmerman, "temporarily" quit his post.
For Wikler, the key date in the story of the Trayvon Martin petition was 22 March, when rallies and marches were launched in New York and several other cities across America. "That's when it shifted from online to offline," he says.
"Before that there had been tremendous buzz around Trayvon's case but it was happening on computers and at dinner tables; then it took to the streets."
That was an important moment for change.org, he says, which exists to facilitate people to do things for themselves. "We are not an advocacy group, we don't join coalitions. Success for us to when other people are successful in changing the world in the way they want to."
The overwhelming potency of the Trayvon Martin campaign, he believes, came from two essential features: the clarity of its story, and the passion and relevance of its petitioners.
"This is the story of a teenager walking home from a store having bought iced tea and skittles for his brother and then he is dead. And his killer isn't charged.
"Add to that sense of basic injustice Trayvon's parents, who now have a direct way to take action."
The fusion of clarity and passion has had explosive results that can be measured in numbers: the petition now stands at 2.16m signatures. But numbers alone cannot convey the wider significance of what has happened this month.
"The petition has given people across the country and the world a concrete thing they could do that would change the story. This was no longer something they were watching on the TV, it was something they themselves were part of," Wikler says.
"That turned the Trayvon Martin story from a tragedy into a movement."