After five minutes,
"Please…don't kill me."
Zen was on his knees, begging Leo to let him go.
As soon as Amy hired Leo, he didn't waste any time as he killed the Ambermane family members, including Zac, leaving only Zen alive.
"If you tell the biggest dirty secret of your Ambermane family, I will let you."
Even if Leo killed Zen now, he would be teleported out. So, he wanted to have something about the Ambermane family which might help him after leaving the [Treasure land].
He didn't want to openly go against the Ambermane family and the City leader's family because he would be killed even before he could take revenge.
Moreover, after Julia's earlier outburst, he was sure that Zola would not let her life once they got out of the [Treasure land].
As for Ryan, even though he left the city leader's group, he was still hesitating about something.
'Ryan, don't do something you regret for your entire life.'
Leo was praying in his heart as he kept an eye on Ryan from time to time.