According to witnesses called at the pre-trial hearing, Pring-Wilson then told Cambridge Police Department officers on the scene that he had observed a stabbing and that he was trying to “help out.”

The motion to suppress claimed that the early statements “were not knowing, intelligent or voluntary”—as admissibility rules require—because at the time they were made the defendant was suffering from post-traumatic stress disorder, a concussion and intoxication.

“The fact that Pring-Wilson made efforts to exculpate himself by his explanations is probative of the voluntariness of his statements,” Grabau wrote in the ruling.

Grabau wrote that a dime-sized welt on Pring-Wilson’s forehead did not affect his ability to make “knowing and voluntary statements” and that he “refused medical treatment and was able to walk home unassisted.”

Also in May, Pring-Wilson’s attorney, Jeffrey A. Denner, filed to withdraw from the case, citing “irreconcilable differences” and “a breakdown in communication” with the defendant.

The trial is currently scheduled for Sept. 13 and attorney Mark Berthiaume, of Boston, is now representing Pring-Wilson.

—Staff writer Hana R. Alberts can be reached at alberts@fas.harvard.edu.