Depending on the nature of the work performed by the employer, they may actually have a duty to follow-up and ask more questions about a person's criminal history, including obtaining a copy of an offense report.  Over the last several years, Washington has beefed up it's awareness of workplace violence issues.  Also, some employers have been sued for "negligent hiring" when they didn't ask enough questions when they knew an employee had violent tendancies.  That is not to say that one assault allegation makes a person a violent risk, but because of the caselaw, they may actually be required to at least give the assault charge a second look to avoid any future liability issues.