George Zimmerman Trial, Day Seven: Enter Instagram

The seventh day of George Zimmerman's second-degree murder trial saw the case's lead investigator, biographer, and medical examiner step up to the stand—and both Instagram and Fox News featured in the prosecution's case. Here's what you know about today's witnesses:

1. Christopher Serino

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Who is Christopher Serino? Serino is the Sanford, Fla. police officer who lead the investigation into George Zimmerman. Initially, Serino drew up a report recommending Zimmerman be charged with manslaughter for the death of Trayvon Martin, but prosecutors ultimately decided to indict Zimmerman with second-degree murder.

What did he testify? Serino agreed with prosecutors that he felt Zimmerman did indeed racially profile Martin on the evening of his death. He added, however, that he thought Zimmerman was telling the truth when he claimed that Martin had attacked him first—and that Zimmerman's account of the evening was credible.

How is this important? The revelation that Serino thought Zimmerman acted in self-defense caused a stir in court: both prosecution and defense agreed that the jurors should not hear opinion in regard to the truth. The judge told the jurors to disregard the statement—the legal version of "let's pretend this never happened."

Serino was the top dog in the investigation, and his opinion holds weight, though the Sanford police have been heavily criticized since the shooting.

2. Valerie Rao

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Who is Valerie Rao? Rao is the medical examiner who treated Zimmerman's injuries the evening Martin died: Feb. 26, 2012.

What did she testify? Rao said that Zimmerman's injuries weren't quite compatible with his account of being repeatedly slammed against the ground by Martin. "The injuries are so minor," said Rao. "The word 'slam' implies great force. There was no great force used here."

How is this important? Zimmerman had testified that Martin "slammed" him against the ground not just once, but over and over again. Rao claimed she doesn't believe he'd been injured more than once, which strengthens the prosecution's argument that Zimmerman is lying.

4.Mark Osterman

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Who is Mark Osterman? Osterman is self-denoted "best friend" and biographer of Mark Zimmerman, and published a book on the case: "Defending Our Friend: The Most Hated Man In America."

What did he testify? Osterman, to not great surprise, came to Zimmerman's defense. He said that Zimmerman's personal account of the night matched up with his public account, and that when Osterman had driven him home from the police station, he'd seemed "stunned" and "detached."

How is this important? It's not, really. Osterman had already confirmed his firm standing in Zimmerman's camp long before the trial, and his comments provided no new information.

In other Day Seven news, the jury was shown Fox News' interview with Zimmerman, in which the accused described the incident as "God's plan." The state also filed a motion against defense attorney Don West, whose daughter posted an Instagram photo of them together the day her father cross-examined Rachel Jeantel. The picture saw father and daughter eating ice cream, with the caption "We beat stupidity celebration" and the hashtag "#daddykilledit."

Judge Debra S. Nelson has not yet responded to the motion.