setVisibility of Task

How can I atribute visibility and invisibility to tasks.


I have a process started by admin, and he need to start multiple times
when comes to a user Lane, can be start by any user of the group, i need when a user DO the first task of his lane, the process case tasks related can be only viewed by him. and others cases tasks will set invisible to him, up until the case who he was doing finishes by admin.

Thanks before hand.

Peter Grant.