I am aware that Kaito's name(s) can potentially cause confusion, so for anyone unfamiliar, here is a quick explanation!

Kaito (快斗) is his name. The 'o' sound at the end is short.

Kuroba Kaito is also the infamous thief 'Kaitou Kid'. The Japanese word "kaitou" (怪盗) is generally translated as "phantom thief," "mysterious thief," or something along those lines. Romanize it how you wish (kaitou, kaitoo, kaitō, kaitoh), but be aware that the 'o' sound at the end is long.

Basically, the long and short of it is that "Kaito" and "kaitou" are different.