A man aboard a Southwest Airlines flight bound for Los Angeles from Dallas died after experiencing a medical emergency mid-flight, law enforcement sources tell NBC4.

Flight No. 958 to Los Angeles International Airport was in the air Friday morning when a passenger went into medical distress and became unresponsive, according to the source.

CPR was administered to the man during the flight and medics responded to the plane upon its arrival in Los Angeles. Ultimately, the man was unable to be revived and firefighters confirmed the passenger had died, the source said.

It’s unclear what kind of medical emergency the man experienced. The Medical Examiner’s Office identified the man as 22-year-old Rain McMillan Walmsey. His cause of death remains under investigation.

In a statement, Southwest Airlines confirmed a “medical incident involving a customer” occurred on flight No. 958.