The 30th (last) audio file for Sadie's Story is not in the "Mombasa Streets" but rather in the "Data Hive" level (also played by the Rookie). However, it will be in a locked area until you find the 29 audio files in the Mombasa Streets. Once you find those files, play the mission "Data Hive" until you reach the hole to get to Sub-station 9. If you found the previous files, instead of the Superintentation closing off the hole so your cop teammate cannot get through (and ultimately get killed by Drones), he will climb down the hole with you. Continue playing until the cop says something similar to "Wait here, I need to go check something." Follow him and he will reveal his true purpose for coming here and will fight you. During or after the fight, you can scan the phone on the wall next to the dead body to find the 30th audio file. Note, finding the audio file will slightly alter the scene, specifically the part where DARE and the Rookie finds Vergil. Instead of DARE telling the Rookie not to shoot, the Rookie will tell DARE not to fire and instead whistle for Vergil to come out.