A "painstaking investigation" means a thorough and detailed examination of something where great care and effort is taken to gather all the necessary facts and evidence. Full definition
After four years of painstaking investigations by this paper, we can reveal authoritatively that at about 4 pm on 17th August, 1993, an argument broke out between the NPP stalwart and the then 34 year old Obaa Yaa over an issue which is as yet unclear. (ghanapoliticsonline.com)
Always astute and elaborate, her technique for creating space may at first sight seem random, but is clearly the result of painstaking investigation, premeditation and control. (artlead.net)
Through a painstaking investigation we exposed the university's shares in apartheid South Africa, and eventually forced their sale. (politics.co.uk)