First link is to the Justice Department press release, second link is to the actual criminal complaint.
The complaint was filed in the United States District Court for the Northern District of California at the San Francisco Courthouse. The case name is United States of America vs. Ali Alzabarah, Ahmad Abouammo, and Ahmed Almutairi, aka Ahmed Aljbreen.
Ahmad Abouammo is an American citizen and is in custody. The other two are Saudi nationals and are in Saudi Arabia and likely have escaped justice.
Two of the individuals, including Abouammo, worked at Twitter and used their positions to unlawfully spy on accounts critical of Saudi Arabia, sending that information back to Saudi Arabia. The third individual assisted the other two.
The suspects are charged with Acting as Agents of Foreign Government without registering with the Attorney General and Destruction, Alteration or Falsification of Records in Federal Investigation, in violation of 18 USC 951 and 18 USC 1519, respectively. The second charge was due to their attempt to launder the payment money. The first charge carries a prison term up to 10 years. The second charge carries a prison term up to 20 years.
The full facts of the case can be found in the criminal complaint.