He decides that he is the closest person who can help, and there's no time to find others.

Theron ran to the victim's rescue, drawing his sword and raising it up into the air to ready the first strike. The muggers noticed his attempt to attack and immediately turned there focus and attacks to Theron. The muggers ganged up on Theron thinking some one so young couldn’t be very strong. Theron brought his sword down in a vertical slash. His target dogged, but didn’t recover his balance in time, for Theron's second blow delivered a severe gouge to his chest. The other muggers attempted to fight Theron as well, but they were unsuccessful in harming him majorly, only managing to cover him with a few shallow cuts.
Though the muggers outnumbered Theron, they didn’t expect the expertise in fencing ability, which Theron had built up over years of being with the mercenaries. Their inability to land any major blows to Theron eventually caused the last few muggers to run away.
Once they had retreated, Theron moved his attention to the victim, and to Theron's surprise, it was Kass.
“Kass are you alright?” Theron asked, his heart beat speeding up as he examined Kass, and to his displeasure, finding that he had been cut a few times.
Kass replied, “Of course I’m not ok…but compared to how much worse I could have ended up I guess I’m alright..." He paused and then added, almost as an after thought, "Thanks.”
Theron lead Kass to the Tavern, where he bought him a late breakfast.
They sat in silence for a while.
Theron had felt a sense of dread when he'd realized that Kass had been those muggers' vitcim. A strange emotion had raced through him.
He cared about Kass, and he wanted to help him remember his past, but after his responce last time, Theron didn't want to risk angering Kass by trying to **** the memories.
He realized, though he didn't want to, that Kass may never regain his memories. Perhaps getting to know who Kass was would be good.

“So where do you come from, Kass?” He asked, breaking the silence.
Kass looked up from his meal before responding slowly, “I don’t know. I remember waking up in a forest with a bunch of cuts and bruises.” Kass replied calmly.
“When you said you would just end up hurting me yesterday, what did you mean?” Theron asked
Kass paused before answering, almost as if weighing his words. “Because every time I get close to some one, they get hurt. I don’t know why, it just happens,” Kass replied before asking a question of his own suddenly. “So... this Alexander... How good of a friend was he? What was he like? Why is he so special?”