She threw him under the bus because the police were already on the trail. Instead of arresting both men, the police stopped at the nephew and let the husband go.
It is implied is that her childhood friend, the policeman wanted to give the husband a second chance and stopped the investigation at...
Now that I think about it, since they're both in the same class, how does MC not know Hiro's surname especially when it's the same as the girl he likes?