"Closer investigation" refers to a careful examination or scrutiny of something to gain a better understanding or discover more details that might not be immediately obvious. Full definition
His landscapes initially seem grounded in our world but upon closer investigation reveal themselves to be fantastical, as if imagined by the protagonists that inhabit them. (pacegallery.com)
What is the process for closing an investigation if the investigation does not reveal a violation of securities or related laws? (globalinvestigationsreview.com)
In the last three years, some 2 % to 4 % of investigated complaints have been closed investigations with diversion. (slaw.ca)