Understanding of a sentence from Death Note


The original sentence is:

> 今までに明らかになった被害者と思われる心臓麻痺死者の全ては、日本で情報を得る事が可能だった者と裏付けが取れました

I think **〜者と裏付け** is the abbreviation for **〜者という裏付け**. And my question is:
should I add a **だ** behind **〜者** , so that the sentence becomes:

> 今までに明らかになった被害者と思われる心臓麻痺死者の全ては、日本で情報を得る事が可能だった者 **だ** と（いう）裏付けが取れました？

I think the modified sentence is more natural. Is it? Or did the original
sentence just omit the **だ**?




You are right, と and という are interchangeable here. And it's generally safer to
keep だ before this type of と, although it's often dropped in reality. Omission
of this type of だ is sometimes called **だ抜き** , and some people frown upon it
if it happens in formal text. See the following article from NHK.

  * [「だ抜きことば」？](https://www.nhk.or.jp/bunken/summary/kotoba/term/140.html)

But also note that there are similar but different cases where だ _can_ be
omitted safely. See the discussion here: [Difference between だと vs と before
認める](https://japanese.stackexchange.com/q/55990/5010)




You are right, と and という are interchangeable here. And it's generally safer to
keep だ before this type of と, although it's often dropped in reality. Omission
of this type of だ is sometimes called **だ抜き** , and some people frown upon it
if it happens in formal text. See the following article from NHK.

  * [「だ抜きことば」？](https://www.nhk.or.jp/bunken/summary/kotoba/term/140.html)

But also note that there are similar but different cases where だ _can_ be
omitted safely. See the discussion here: [Difference between だと vs と before
認める](https://japanese.stackexchange.com/q/55990/5010)

