Published: Apr 22, 2010 8:31 PM EDT

 FORT LAUDERDALE, Fla. - An attorney representing a teenager accused of severely beating a girl at a South Florida middle school says he has entered a written plea of not guilty on behalf of his client.

Wayne Treacy, 15, is accused of trying to kill Josie Lou Ratley at a Deerfield Beach Middle School campus bus stop on March 17, 2010. He is charged as an adult with first-degree attempted murder.

Attorney Russell Williams has not denied Treacy's role in the assault and has signaled a defense strategy that will focus on Treacy's mental health.

Ratley suffered brain damage in the assault and is still unable to speak. She is hospitalized and underwent a third brain surgery earlier this week.

Related: Fla. Girl attacked at school leaves hospital

Florida teen's attacker to be charged as an adult

Josie Lou Ratley emerges from coma

Mother of Fla. beating victim says teen showing progress