Killed is the past tense of kill--an action verb.
kind of sort of not really
Yes, 'was killed' is a compound verb. A compound verb consists of an auxiliary verb (was) and another verb (killed).
The verb in that expression is "killed."
Yes, the word killed is the past participle, past tense of the verb to kill (kills, killing, killed). The past participle of the verb is also an adjective, a word to describe a noun, for example a killed virus, a killed flame.
A linking verb.
A linking verb
It is an irregular verb.
The verb appear can be a linking verb or an action verb.
An auxiliary verb
the infinative
It is a regular verb
Is becomes a verb