Why is the military prosecuting this case?

The Rapid City Journal (US) reports on the Article 32, UCMJ, preliminary hearing of an airman accused of murdering his child.

Cunningham was arrested and charged March 3 by the Rapid City Police Department with aggravated child abuse for punching the baby in the head. The Pennington County State’s Attorney Office upgraded the charge to second-degree murder when the infant died nine days later after being airlifted for treatment at a hospital in Sioux Falls.

Cunningham had already made several appearances at the Pennington County Court when the Air Force requested to take over the case in early May, said Lara Roetzel, chief deputy at the state’s attorney office.

The Air Force can take jurisdiction over cases involving airmen even if the crime occurred off base, Roetzel said. The office consented to the transfer because it's already crunched for time due to coronavirus-related furloughs.

The Air Force works “towards maximizing jurisdiction over our airmen,” Lt. Joshua Sinclair, an Ellsworth spokesman, said when asked why the Air Force wanted the case.

Interestingly, the US military is also affected by COVID-19. Only now are courts started to work after an approximate three month hiatus.