The original manuscript is not extant for crime(s). Either the singular crime or the plural crimes would fit within the lacuna. And even if 𝓞 read as crime, it still could have been an error for crimes. See the discussion under Alma 30:11 for an example in 𝓞 where Oliver Cowdery initially wrote crime instead of crimes.
The problem with the singular crime is that the discussion here in Alma 50:39 is a general one. The wicked have usually committed more than one crime. Moreover, the reference here is to a plurality of individuals, and they would not have committed the same crime. All other general references to crime committed by individuals have the plural crimes rather than the singular:
Of course, in English the word crime can be used in a noncount sense, as in “some people have committed a lot of crime in their lives”. Thus one could argue that the singular crime works here in Alma 50:39 since it can be given a noncount sense. For that reason, the critical text will accept the singular crime in this instance. Nonetheless, the possibility remains that the original text actually read in the plural as crimes (given that in all other instances the noun crime is used as a count noun in the Book of Mormon text).
Summary: Maintain the singular crime in Alma 50:39, the reading of the earliest extant source (the printer’s manuscript); the word crime can be interpreted here in a noncount sense, thus permitting the singular; usage elsewhere in the text argues for crime as a count noun, which suggests that the original text may have read crimes here in Alma 50:39.