Public service agency Internal Affairs units are notoriously underfunded and overworked. Often times their internal cases take a tremendous amount of time, exacerbated by a common lack of proof on either side of the allegations made.
Government is exempt from the Employee Polygraph Protect Act (EPPA) rules, so many public agencies choose to use polygraphs in internal affairs investigations. Around 65% of police agencies use them, for example. Case law for your particular jurisdiction must be reviewed first.
If you are an Internal Affairs unit chief, PPoT would be happy to engage with you to discuss how polygraph examinations might work for your team. PPoT has also developed a 8 page easy-reading primer about the topic. Email PPoT today if you are an Internal Affairs director. Also consider reviewing this significant article about liability and consent.