At the beginning of JoJo's Part 5, Jotaro sends Koichi to Italy to find the son of Dio. Koichi. Really? Not saying Koichi isn't capable but if his suspicion of Dio having a spawn was correct, wouldn't Jotaro take this family business into his own hands? Why send Koichi instead of going himself?
Jotaro would've been sensed by Giorno if he had gone to Italy. People with the Joestar birthmark can feel each other's presence, therefore Giorno would've been alerted by Jotaro and he wouldn't have allowed himself to be observed quietly. Koichi is, according to Jotaro, reliable, so he sent him to observe Giorno and determine whether or not he was evil or dangerous without being spotted immediately.