Here we have a large omission in the 1841 British edition, the result of the typesetter’s eye skipping from the first slay them to the second one. The 1849 LDS edition restored the missing text. Of course, the critical text will follow the earliest reading.
Summary: Maintain in Alma 44:17 the clause that was accidentally omitted in the 1841 British edition, “and it came to pass that they began to slay them”.