How were these holes milled? Picture included

[Micro Milling]

Here is a picture of an antique cut away lock that I have. Somebody made the cutouts as you can see in the pictures below. How were these cuts most likely made?

You can see some of the markings, maybe some of you can tell me what was used? Any other information on what you can determine from the cuts on the brass would be very helpful.

What I don't understand are those diagonal markings.

Thanks for any help.

[Geof]

My guess is that a little hole was drilled, you can see what looks like part of a hole in the pictures, and then it was cut out with a tiny saw.

[extanker59]

Just a guess. It looks to me like the diagonal marks are from a file. You know, file to fit.

[DareBee]

Looks like a hand job to me.

Drill, saw and file

[RICHARD ZASTROW]

Cast, file to remove flash & fit. Just like us old farts did. LOL

Dick Z

[neilw20]

I am not the only file and hacksaw man.
Them is file marks.