What are the consequences if a border guard kills a Muslim infiltrator after chasing and shooting him, and does this necessitate expiation (kaffarah), blood money (diyah), or retribution (qisas)?

Willful killing is one of the gravest sins, and Allah has promised a severe torment for its perpetrator. However, the killer's repentance is accepted if it is sincere. Along with repentance, the killer must offer expiation for the killing and blood money to the victim's family. The expiation is the freeing of a believing slave or fasting for two consecutive months. As for those who aid in killing, there is no retribution (qisas) upon them unless they aided with the intention of killing and caused its occurrence. Even if the victim was in error, that does not permit their killing.