LOS ANGELES — George Zimmerman, a neighborhood watch volunteer, faces second-degree murder charges for shooting Trayvon Martin, an unarmed black teenager in Sanford, Fla., the special prosecutor in the case announced Wednesday.

In a televised news conference, Florida State Attorney Angela B. Corey outlined the charges in the case that has sparked national demonstrations calling for Zimmerman’s arrest.

“I can tell you we did not come to this decision lightly,” Corey told reporters. “We do not prosecute by public pressure.”

She said that her office had filed an information with the charge.

Zimmerman, who has maintained he acted in self-defense, was in custody in Florida, Corey confirmed, though she gave no further details. He had been in hiding since the shooting after his family said he had received death threats.

Martin, 17, was returning from a convenience store run on Feb. 26 — he had bought a bag of Skittles candy and an iced tea — when he caught Zimmerman’s eye. Zimmerman, 28, was driving out of his gated community in Sanford on his way to the supermarket when he called the Sanford Police Department to report a young black male acting suspiciously, possibly on drugs, he said.

The police dispatcher asked Zimmerman if he was following the youth. When Zimmerman replied that he was, the dispatcher told him: “We don’t need you to do that.” Moments later, Zimmerman — armed with a 9-millimeter weapon — got out of his car.

Zimmerman has said he shot Martin in self-defense after the youth struck him in the face, knocked him down and began pounding his head into the ground. But many believe Zimmerman was the aggressor, emboldened by his status as the neighborhood watch captain.

Coverage of the case was largely limited to local media until the call between Zimmerman and the dispatcher were made public, along with a 911 call that one resident made just before the shooting. In the background of that call, someone can be heard yelling for help. Martin’s parents insist that voice belonged to their son. Zimmerman has said the voice was his.

The phone calls and steady stream of new evidence, not to mention potential evidence, has turned many Americans into armchair CSI experts.

But the case itself struck a chord — and not just within the African-American community. Many Americans consider it cut-and-dried evidence of the social injustices that blacks in this country have long faced.

The intense media attention has been propelled in part by outrage in the social media world. Twitter has been flooded with Tweets and an online petition at Change.org demanding Zimmerman’s prosecution has received more than 2.2 million signatures — the single biggest reaction the online petition platform has ever had.

In the wake of such scrutiny, as well as marches, protests and rallies held across the county, the U.S. Department of Justice and the FBI have launched probes into the case, and a special prosecutor has been assigned to review the matter. The case even gained the attention of President Barack Obama, who called for a thorough investigation.

And, no surprise, the case has also stirred up a backlash against the media attention.

A recent survey by the Pew Research Center for the People & the Press found that many people — including a majority of Republicans surveyed and 43 percent of whites surveyed — said the media had gone overboard in its coverage.