N1
ずにはおかない
Will definitely, Will certainly, Bound to, Not fail to
メディアにも取り上げられたから、警察も調査をせずにはおかない。
Since it was covered by the media, the police will certainly investigate.
Explanation
「ずにはおかない」 has 2 uses
1Won't rest until
With a person as subject: a firm resolve to do it and not stop until it's done.
小説、勇者：「どんな手段を用いても、かならず魔王を倒さずにはおかない。」
Novel, Hero: 'No matter what it takes, I will not fail to defeat the Demon Lord!'
メディアにも取り上げられたから、警察も調査をせずにはおかない。
Since it was covered by the media, the police will certainly investigate.
2Can't help but make
With a work, words or an event as subject: it is so strong it is bound to stir a feeling or reaction, usually with the causative ～させずにはおかない.
あの人のスピーチは聞く人を感動させずにはおかない。
That person’s speech will not fail to move the audience.
この映画のラストシーンは、見る人を泣かせずにはおかない。
The last scene of this film is bound to make viewers cry.