The corrected line is as follows:
Yeah, the only catch is he needs to, um, charge his batteries with teenage girls; Asian ones, apparently… We had him on 8 counts of statutory in Pennsylvania, but he went underground in April.
Statutory is short for statutory rape, a legal term in some jurisdictions referring to sexual activity where one participant is below the age legally required to consent to sexual contact. (The legal treatment is rather more complicated, but this fact is not a central plot point, nor from what I can tell does the show strive for perfect accuracy in legal matters.)
Law enforcement had "Holy Wayne," the character they are speaking of, in the sense that they maintained an advantage over him. One may infer that they had collected enough evidence or testimony to charge him with 8 cases of statutory rape in Pennsylvania.
Before they could apprehend them, however, he went underground in the sense of going into hiding, especially from the police or other authorities.
If he had been arrested by the police, they would not have said he had gone underground. If he were in jail, he would have simply escaped; if he had been released on bail, he would have jumped bail.