It should also be noted to unlock this achievement when you go back to your apartment and look at the board of feathers.

Thank you

Nice screenshots guide !
Here are a few details about the feathers locations :
Monday 1 - Chapter 4 : First staircase on the way to Halperin's office, under your feet
Monday 2 - Chapter 6 : In Fairfax family's house bathroom
Tuesday 1 - Chapter 9 : Before entering Halperin's office, head back to corridor
Tuesday 2 - Chapter 10 : In the morgue far right corner, before touching the red bird
Wednesday 1 - Chapter 17 : In Fairfax family's house office, on the left of entrance
Wednesday 2 - Chapter 18 : In the bar entrance, under your feet
Thursday 1 - Chapter 19 : Halperin's apartment, first room on the left downstairs
Thursday 2 - Chapter 20 : Interrogation room, in the corner behind your back
Friday 1 - Chapter 27 : Lift to Halperin's apartment, under your feet
Friday 2 - Chapter 29 : Water top tower, on the way to meet Halperin
Hope this helps :-)

Great guide! Thank you.
A couple of comments would have been nice, though. For instance, picture number 2 on Wednesday: the tile does not make me immediately remember that it is found in the bar. Or Tuesday, number 1: a good advice is to turn back immediately when we stand in front of Maria's office as it is back in the corridor.

Thanks again!!

How did u get all achievs?

Corrected, missed it accidentally.

Нет одного пера, когда вы появляйтесь в баре сразу же посмотрите под ноги, там будет еще одно перо.

No one feather, when you show up at the bar as soon as look at his feet, there will be one more feather.