The Seraph Squad are a group of S Models robots that work as some sort of law enforcers. They have a base at Long Acre Warehouse 113. They appear to be very bad at lying, and all they can do is attempt to contradict the truth (No secret base here!).
In their first appearance two of them are shown talking in some incomprehensible language. When Annie spots them they run away in to the Robot Infrastructure.
The Seraph Squad had apparently been on the search for Robot ever since he was broken out of the Robot Infrastructure in Chapter 12. They do capture him at the end of Chapter 41: Changes , but later in that chapter they release him of all charges as well as starts keeping an eye over Katerina Donlan as they are convinced she is an angel.