corroborative investigation; search for supporting evidence
Used in legal, police, or journalistic contexts for an investigation aimed at finding evidence that backs up a claim or suspicion.
The police are conducting a corroborative investigation to verify the suspect's statement.
裏付け means 'supporting evidence' or 'backing' itself, while 裏付け捜査 is the investigative process of obtaining such evidence.
捜査 is a general 'investigation' or 'search', whereas 裏付け捜査 specifically focuses on finding corroborative evidence.
Compound of 裏付け (うらづけ, 'backing, supporting evidence') and 捜査 (そうさ, 'investigation').