Because the cases range from 6 months to 2 years ago, it is hard for the police to get definite evidence on the case. The woman who claimed the date to be December last year has so far submitted her therapy session the day after her sexual assault, as well as the texts she sent to her close friends referring to Yoochun by his real name, as evidence.
Today (6/20), Yoochun will be filming his own legal rebuttal against the women saying he is innocent, but the police will still be paying special attention to the case as all four women are adult entertainment business workers, and that all four cases happened in a bathroom.
Even if he did not sexually assault them, the case that he illegally bought sex is still very possible, especially if the DNA on the first woman's underwear turns out to be Yoochun's. However, it is still hard to prove that the money he paid to the bar included the sex, so the police will have to hold a corroborative investigation.