Benning: Evidence is a Mass Effect 3 side mission that can be completed only after Cerberus Abductions N7 Mission, but you can start it earlier.
When to start
After Priority: SurKesh
“Ambassador Dominic Osoba is looking for evidence of his son, lost during a mission on Benning.
Find evidence of what happened to his son and return to the ambassador.”
The mission is received from Ambassador Dominic Osoba.
You will find Osoba, if you visit the Citadel Embassies.
When you exit the elevator turn left and you will see him near the window.
This mission must be completed before Priority: Tuchanka.
Assuming that you have finished N7 Cerberus Abductions and you have missed the Dog Tags, go to the Spectre Office, in the Embassies area and check the terminal.
Purchase Information on Bilal Osoba, and then go back to the Ambassador to finish the mission.
If you have the Dog Tags give them to Dominic Osoba.
Next side-mission: Athena Nebula: Hesperia-Period Statue.