Cannot delete files from /sdcard topic

hi everyone,
I cannot delete two files from a folder on my sdcard which I put there via adb.

Code:

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C:\>adb shell ls -l /sdcard/!flash
-rw-rw---- root    sdcard_r 253358134 2015-01-25 23:33 cm-12-20150124-NIGHTLY-mako.zip
-rw-rw---- root    sdcard_r 230777289 2015-01-25 23:33 pa_gapps-modular-mini-5.0.1-BETA12-20150116-signed.zip

C:\>adb shell ls -n /sdcard/!flash
-rw-rw---- 0        1028    253358134 2015-01-25 23:33 cm-12-20150124-NIGHTLY-mako.zip
-rw-rw---- 0        1028    230777289 2015-01-25 23:33 pa_gapps-modular-mini-5.0.1-BETA12-20150116-signed.zip

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i cannot change permissions or owner, whatever i try either with adb or terminal emulator.
they take up ~500mb, so it would be really nice if they were gone.
does anyone have an idea other than data wipe? would be greatly appreciated!