So the cops on this show are terrible like why would a kidnapper ever run to a child and scream his/her name in…
It was Seojin's plan after she pasted the missing child poster on his door. She was caught on cctv and he recognized her. He took it as a threat and placed cops at the venue to catch Aeri red-handed
And I think if she tells him his wife is cheating their trust can be broken and they can't help each other.