This is the 9733rd most frequent Korean word.
고발인의
"Of the accuser" or "pertaining to the informant."
In this sentence, '고발인의' (gobalin-ui) is used as possessive and describes whose evidence is being referred to, associating it to the accuser.
고발인의 증거는 굉장히 확실해 보였다.
The accuser's evidence seemed very compelling.
Here, '고발인의' modifies '진술' (testimony), indicating the person providing the testimony, which is the accuser.
법정에서 고발인의 진술이 클라이막스였다.
In court, the accuser's testimony was the climax.
In this context, '고발인의' qualifies '진술서' (written statement), indicating the ownership of the statement missing from the records.