remove posts on thread display via plugin

[zbaig]

hi all,

i want to exclude some posts of one user on thread.

for example one thread is having tid = 149 and posts greater than 20.

i do not want to show posts of uid = 44.

i want to do it via plugin.

1. what hook will be used?
2. and how i can change query or existing functionality of thread display?

any quick help or any guide line.

i do not need whole coding, just the specific idea, hint, code etc.