ORLANDO, Fla. -

New evidence shows the neighborhood watch volunteer charged with killing Trayvon Martin giving a voice identification test.

The recording released Wednesday shows George Zimmerman yelling "help" several times.

Prosecutors wanted to compare that voice test with shouts for help than can be heard on 911 calls reporting the confrontation between Zimmerman and Martin last February at a gated community in Sanford.

AUDIO: Zimmerman recording

Zimmerman is charged with second-degree murder but is pleading not guilty.

Zimmerman has a bond hearing Friday during which he will ask a judge to grant him bail a second time. His $150,000 bond was revoked earlier this month after prosecutors say he and his wife misled the court during an April bond hearing.

Zimmerman's is asking that he be allowed to wear civilian clothes at the hearing.