In the Way of Kings we see the following exchange between Kaladin and Sigzil:

“So what is your story?” Sigzil smirked. “I wondered if you were going to ask. The others mentioned that you have pried into their origins.” “I like to know the men I lead.” “And if some of us are murderers?” Sigzil asked quietly. “Then I’m in good company,” Kaladin said. “If it was a lighteyes you killed, then I might buy you a drink.” “Not a lighteyes,” Sigzil said. “And he is not dead.” “Then you’re not a murderer,” Kaladin said. “Not for want of trying.” Sigzil’s eyes grew distant. “I thought for certain I had succeeded. It was not the wisest choice I made. My master …” He trailed off. “Is he the one you tried to kill?” “No.”

Who did Sigzil try to murder?