Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
investīgātĭo, ōnis, f. [investigo], a searching or inquiring into, investigation (class.): rerum occultissimarum, Cic. Fin. 5, 4, 10: veri (with inquisitio), id. Off. 1, 4, 13: sapientiae ejus, Vulg. Isa. 40, 28.