Hide checkbox in Web portal after it's set to true

Hi.

Im currently working on a solution to tick a checkbox in the web portal. 
I want the checkbox to be visible to a certain group of people (this is done with Group permissions and role permissions). The Permission group is called "Checkboxadmin".
I also want the checkbox to be read-only after it is "true" for everyone except a certain group of people. As of now, it shows as read-only, but this is both when checkbox is ticked or not. For all others it says "hidden: checkbox" (i want this gone aswell). The checkbox should be completly gone for every other user except the group "Checkboxadmin".

So, in the Restrict property to be read-only i have this WebSQL:

Exists("Person",
            SqlAnd(
            sqlCompareUID("UID_person", GetUser()),
            SqlCompare("checkbox", "True", "bool", "Equal")
)
)

Is GetUser() the user chosen in the portal or the loggedin user? 

Any ideas?