During a battle with an NCR force, he chose to be captured instead of committing suicide, counting on being able to escape captivity without revealing any information about Caesar's plans. The player can try to interrogate him at Camp McCarran during an unmarked side quest.
Silus Treatment: Silus is held captive in Camp McCarran, and the NCR is attempting to interrogate him. He will not give information to the NCR, and interrogator Carrie Boyd is looking for help. She informs the player that the NCR does not allow torture of prisoners. The player can suggest a truth serum, beating the prisoner, or calling him names. Silus may also be freed by a Legion-oriented player, resulting in a few special dialogue lines from Caesar.
After Silus is dressed as an NCR corporal, he will not speak to you while he leaves.
It is possible to pickpocket Silus' centurion armor once he is wearing the NCR uniform.
Killing Silus when he's still being held in custody will not result in Caesar's Legion infamy.
Silus's name is strangely pronounced different by different characters, Lt. Boyd pronounces it See-LOOS, while Caesar pronounces it Cy-LUS. The difference in pronunciation is common between Latin and English. Fluent Latin will cause a 'c' to always be pronounced as if it were a 'k'. (Such as 'Caesar' being pronounced as "SEE-sar" in opposition to "KYE-sar") This pronunciation is used to a supremacy-level across Caesar's Legion, as they even inherit the pronouncing of Latin words and names in fluent Latin when speaking in English.
"Let's see. I know that you're a brainless cretin. I know that you're wasting your time. I know the lieutenant is going to be disappointed in you. And I know that by this time next month the streets of New Vegas will be decorated with the decaying heads of NCR soldiers. Is there anything else you wanted to know?"
"I train my men to make sure the slaves' flesh bulges a bit around the top and bottom. Know why? It cuts in just enough when they swallow or turn their head to remind them who they belong to. And it's that constant reminder that keeps them docile."