고소인이 · 고소인을
complainant (in a criminal complaint)
Example
고소인은 경찰서에서 피해 사실을 자세히 진술했습니다.
The complainant described the harm in detail at the police station.
Word parts
고 report+소 sue+인 person
-인 = person in a legal role: 고소인, 피고인, 변호인.
Good to know
고소 is filed by the victim; 고발 is filed by a third party who isn't the victim.