He killed 同 He was killed

He killed 唔會解左做被動的。
因為passive voice被動式動詞的基本形式就是
verb( be ) + verb in p.p.
所以一定係 He was killed by someone.
He killed by someone. 在文法上是錯的。

另外，動詞轉pp的確是可轉做形容詞的。
至於加ed就轉做形容詞，是因為那個verb是規則動詞，加ed就是該動詞的pp. 如果是不規則動詞如break, 它的pp是broken, 就可作形容詞用。
所以定義上是轉pp變形容詞，是否加ed轉形容詞全在乎那個verb是否規則動詞而已。

he killed一定唔會解左做被動
最簡單既被動係一定要係 subject + be + p.p.
亦都唔會寫做 he killed by someone
一定係 he was/is killed by someone

the man he killed = the man (whom) he killed
但係whom我地可以唔寫
而whom he killed係adj. phrase
用一個phrase黎形容man

p.s. the man he killed 唔可以係一句
因為呢句得subject 冇 main verb
例如: the man he killed is his enemy.