This is the 8982nd most frequent Russian word.
расследование
Investigation.
The word 'расследование' here refers to a systematic examination or inquiry into the reasons behind an accident.
Ведётся расследование причин аварии.
An investigation of the accident's causes is ongoing.
In this sentence, 'расследование' signifies a formal investigation into a case, typically conducted by law enforcement or legal authorities.
Он принимает участие в расследовании уголовного дела.
He is participating in the criminal case investigation.
Here, 'расследование' describes an inquiry conducted independently by an individual to uncover information about corruption.