What is the grammar form with "にした" in this sentence?


I have another sentence from 合格できる、日本語能力試験N２:

> そこで私はいつも考えるのだが、各国にある日本大使館は日本人旅行者のため、こういう留学生、研究家を講師 **にした**
> 講座を現地で開いてくれないだろうか。

The part in the sentence where it says 「講師にした講座」 is hard for me to understand.
I wondered why it cannot be 「講師にして講座」. Is there some grammar form in this
sentence that explains why it should be 「講師にした講座」?




  * Traditional grammar says (stupidly) that it is the 連体形 of the 助動詞 た.
  * Some modern linguists say it is the past attributive form (連体形) of する used in a relative clause.
  * I believe it is the past morpheme (attached to the stem of する) used in a relative clause.




  * Traditional grammar says (stupidly) that it is the 連体形 of the 助動詞 た.
  * Some modern linguists say it is the past attributive form (連体形) of する used in a relative clause.
  * I believe it is the past morpheme (attached to the stem of する) used in a relative clause.

