This is the 12425th most frequent Korean word.
당국에
"당국에" means "to the authorities" in English.
Here, '당국에' is used to indicate that an action (reporting) should be directed towards the authorities.
당국에 신고해야 합니다.
We need to report this to the authorities.
In this sentence, '당국에 의해' (by the authorities) shows that the action of investigating was carried out by the authorities.
이 사건은 당국에 의해 조사되었습니다.
This case was investigated by the authorities.
The use of '당국에' specifies that the assistance is expected from the authorities.