I also vote for wipes. Just like how diamonds are still sometimes a valid thing to steal and fence (nope, trade too closely controlled, not plausible even by the 70s) lots of movies either take their inspiration from or are direct movie versions of old books. Sometimes they do period pieces, but too often they skip that for budget but never really update the script. So, no one /really/ has a mobile phone in 2023 for example.
The book the movie (already a remake of a euro movie which may be better) is based on was first published in 1985, toss in a decade for out of date tech as is the way and 1970 suppressors: sure, wipes.
B&T still makes a (very very quiet) dedicated suppressed pistol with wipes, FWIW:
Anyway, old school wipes were quite consumable and /I believe/ this line more or less makes sense not from wipe wear but residue. Suppressors were never super common so it would be a lot more like a
clue than the fingerprint that bullet comparitors are supposed to give us. .32, suppressed: probably our guy.