GREENSBURG — A hearing is scheduled next month on a request to transfer a 16-year-old boy to a mental health treatment facility while he awaits trial in a mass stabbing at a Pennsylvania high school last spring.

Defense attorney Patrick Thomassey wrote in a June motion that Alex Hribal of Murrysville continues to “deteriorate” in the Westmoreland County juvenile detention center, where he has been held since his April 9 arrest.

A hearing is scheduled Sept. 26 in Westmoreland County Court on Thomassey’s request to move the youth to Adelphoi Village, a secure residential treatment facility in Derry Township.

Hribal is charged with stabbing 20 fellow students and a security guard at Franklin Regional High School. Four students were critically injured, but all have recovered.

He is facing 21 counts each of attempted homicide and aggravated assault.