“Qatl” is the verbal noun: the action of killing conceived nominally.
“Qatala” is a past-tense verb: it presents that event as occurring in the past.
“Qātil” is an active participle: it characterizes an agent through the act.
The forms share a root, but the kind of borrowed expression differs. A nominal transfer can be analyzed as original, whereas a verb or derivative contains a dependent assignment of the transferred meaning.
Sharing a root is therefore not sufficient to assign the same metaphorical category to every form.