點解這裡會用being可否用is呢?

你這條問題實在是一條非常好的問題，它涉及的範疇是“動名詞”
首先我要指出after在這裏並不是作連接詞conjunction用，而是作介系詞preposition用，因著preposition之後必須是名詞（或名詞相等用語），所以，在這句就用了動名詞。

After being arrested by police office原本是：After his being arrested by police office，但因為與主要子句的subject相同，那就可以把his省略；但若主要子句的subject與動名詞意思上的主詞不相同的話就不可以省略，如：He insisted on my going there（他堅持我要去那兒）的my與He是不同人就不可以省略。但He insisted on (his) going there(他堅持要去)的his就可以省略。

現在想你已知道 (his) being arrested是動名詞，那麼我們就要知道動名詞是怎樣形成；動名詞是：原形動詞+ing作為名詞用，如：reading novels的reading就是動名詞；Lying late的Lying就是動名詞。而動名詞的被動語態，是由：being+過去分詞所組成，如：I don’t like being spoken to like that（我不喜歡那樣被談論）的being spoken to就是動名詞的被動語態。

現在你大約知道動名詞的被動語態怎樣形成，想，你現在也知道為甚麼不可用“is”或“was”之類。

這裡其實是兩句句子合併成一句的:
The 36-year-old man was handcuffed. The 36-year-old man was arrested by police office.
-->The 36-year-old man was handcuffed after he was arrested by police office.
-->The 36-year-old man was handcuffed after being arrested by police office.

"(subject) + WAS (IS) arrested" = "(no subject) + BEING arrested"

係呢句句子內, The 36-year-old man : '36-year-old' is an adjective, to describe the man

...after being arrested : We can't use 'is' because it is 'after' 之後, we need to use 'ing' form , 而'is' 的'ing' form 就係 'being'

明否? Attention!!! 我未必一定對的!!!

吾能，因為係reduced clause，用吾到main verb 嫁。