(CNN) -- The second-degree murder charge George Zimmerman faces in the killing of 17-year-old Trayvon Martin surprised some observers, but it's typical in "heat of passion" slayings, a Florida defense lawyer said Thursday.
Special prosecutor Angela Corey was closed-mouthed about the evidence supporting the charge when she announced it Wednesday. But Assistant State Attorney Bernie de la Rionda, who spoke at Zimmerman's first court appearance Thursday, told reporters that prosecutors "only file charges we can prove."
CNN Senior Legal Analyst Jeffrey Toobin said Corey "threw the book" at Zimmerman, a neighborhood watch volunteer from Sanford, Florida.
"This is the single most severe crime he could have been charged with under these circumstances," Toobin told CNN's "Anderson Cooper 360."
But Miami defense attorney Jayne Weintraub told CNN's "Early Start" that she was not surprised by the charge.
"It's typical second-degree murder," Weintraub said. "It's the heat of passion, spur of the moment in the middle of a fight. That's what second-degree murder is typically used for."
Zimmerman told Sanford police he shot the unarmed Martin in self-defense during a fight. He was allowed to remain free until Wednesday, sparking protests and a nationwide debate about race and racial profiling -- Zimmerman is Hispanic, while Martin was African-American.
Natalie Jackson, a lawyer for the Martin family, said the charge seems "appropriate" for the circumstances.
"It's actually a very brave charge of Angela Corey, and it really shows that she conducted an independent, impartial and fair investigation in this case," Jackson said. "She could have easily charged this as a manslaughter, to try to appease everyone, and she didn't. She did what prosecutors do. She charged it to the hilt."
Zahra Umansky, who represented Zimmerman after a 2005 arrest on an assault charge, said the severity of the count came as a surprise to many lawyers.
"We, as a legal community, thought that the charge would be only manslaughter," Umansky told CNN's "Starting Point."
In the 2005 case, Zimmerman entered a pre-trial diversion program and took an anger-management class, Umansky said. In his application for a 2008 law-enforcement program at the Seminole County sheriff's office, he said the arrest stemmed from a case of mistaken identity.
A conviction for second-degree murder carries a maximum sentence of life in prison. Under Florida law, prosecutors who bring a case are expected to show that a death resulted from a criminal act and that the killer showed a "depraved mind" without regard for human life.
Weintraub said that's demonstrated by Zimmerman getting scared "and he goes for his gun."
"When there's no gun, there's nothing facing him except a 17-year-old kid," Weintraub said. And she predicted that an account by Zimmerman's brother -- that Martin had beaten him nearly unconscious -- "won't match the evidence."
And CNN legal analyst Sunny Hostin to CNN that despite the intense scrutiny of the incident, the charge suggests there's more to the case than publicly known.
"I suspect that there is some evidence we just don't know about, because no prosecutor in a high-profile case wants to walk into court and not be able to prove each and every count beyond a reasonable doubt," Hostin said. "You don't want to lose so publicly."
Although details of the evening shooting remain murky, what is known is that Martin ventured out from his father's fiancee's home in Sanford to a nearby convenience store, where he bought a bag of Skittles and an Arizona Ice Tea. On his way back, he had a confrontation with Zimmerman, who is Hispanic, and Zimmerman shot him.
Zimmerman had called 911 to complain about a suspicious person in the neighborhood, according to authorities. In the call, he said he was following Martin. Though the dispatcher advised him against it, Zimmerman pursued Martin anyway before saying he lost sight of him.
According to an Orlando Sentinel story later confirmed by Sanford police, Zimmerman told authorities that after he briefly lost track of Martin, the teen approached him. After the two exchanged words, Zimmerman said, he reached for his cell phone, and then Martin punched him in the nose. Zimmerman said Martin pinned him to the ground and began slamming his head into the sidewalk.
A police report indicated the volunteer was bleeding from the nose and the back of his head, and authorities have said Zimmerman was not immediately charged because there were no grounds at the outset to disprove his account of the confrontation.