Who showed Szeth's oathstone in I-5 WoK?

[An Inkspren]

Interlude 5, The Way of Kings. Szeth is in a gambling den,  he needs to assassinate some minor crime lord, upon arriving at the crime scene he sees someone with his oathstone. The person has his old master dead, and gives him a list of Monarchs. We later learn that his new master is Taravangian. But I don't think this is the person holding his oathstone in I-5. He says "we" as part of a group, and refers to the new "master" as someone else. He also then leaves by soulcasting the wall. So this has to be someone with a soulcaster. I couldn't find who that was but I assume it's a member of The Diagram. 
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[Going_North_cal]

31 minutes ago, An Inkspren said:

Interlude 5, The Way of Kings. Szeth is in a gambling den,  he needs to assassinate some minor crime lord, upon arriving at the crime scene he sees someone with his oathstone. The person has his old master dead, and gives him a list of Monarchs. We later learn that his new master is Taravangian. But I don't think this is the person holding his oathstone in I-5. He says "we" as part of a group, and refers to the new "master" as someone else. He also then leaves by soulcasting the wall. So this has to be someone with a soulcaster. I couldn't find who that was but I assume it's a member of The Diagram. 
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I'm not smart on this subject, but probably not Taravangian himself. Probably a higher up in The Diagram, yes.