It can't be "They killed Molor" because that would require lu-, correct? i.e. "molor luHoH" ?
The contributor team of Klingon highly supports the use of "they" as a gender neutral singular pronoun. However, because the Klingon language makes a much bigger deal of number than of gender, it is more important in teaching Klingon to distinguish number than to distinguish gender. Thus in this course we only accept "they" as a plural pronoun so we can be sure that the learners know when something is singular versus plural.