Ben 10: Detective Cases/Case 34

This is the 34th and case of Ben 10: Detective Cases. This case happened in a sewer, 6 workers got disapeired during their work in the sewer. Other 4 of their co-workers tried to search for them but with no answer.

==So which alien do you think made the crime?(put only one alien untill i tell you that your ans. is wrong!)Edit==