Prosecutors in George Zimmerman's murder trial plan to introduce a surprise witness today: the girl who Trayvon Martin was on the phone with shortly before the confrontation that resulted in his death. Zimmerman, 29, was charged with second degree murder last year after fatally shooting the 17-year-old Martin outside of the Retreat at Twin Lakes community in Sanford, Fla.

The witnessknown as Witness #8 or "Rachel"—has provided written testimony that Martin was afraid the night of his death, and that she told him to run away from Zimmerman. Zimmerman's defense team finds itself on its heels entering the second day of the trial; yesterday, defense attorney Don West failed miserably with a "knock-knock" joke during opening statements:

"Knock knock. Who's there? George Zimmerman. George Zimmerman who? Good, you're on the jury."

Nobody laughed. West would go on to explain to jurors that Martin attacked Zimmerman, leaving him with no choice but to shoot the teen in self-defense. If convicted, Zimmerman could face life in prison.

[via Gawker]

RELATED: The Complete Timeline of the Trayvon Martin Case