Abdulhakim's father is now speaking out.
Notice Abdulhakim said that what he did wasn't murder, since murder only applies to killing without justification. What's the justification for killing soldiers who will be traveling to Muslim lands?
Qur'an 5:33—The punishment of those who wage war against Allah and His apostle and strive to make mischief in the land is only this, that they should be murdered or crucified or their hands and their feet should be cut off on opposite sides or they should be imprisoned; this shall be as a disgrace for them in this world, and in the hereafter they shall have a grievous chastisement.
While we're on the topic of violence in Islam, we probably shouldn't leave out:
Qur’an 9:29—Fight those who believe not in Allah nor the Last Day, nor hold that forbidden which hath been forbidden by Allah and His Messenger, nor acknowledge the Religion of Truth, from among the People of the Book, until they pay the Jizyah with willing submission, and feel themselves subdued.
Qur’an 9:73—O Prophet! strive hard against the unbelievers and the hypocrites and be unyielding to them; and their abode is hell, and evil is the destination.
Qur’an 9:111—Surely Allah has bought of the believers their persons and their property for this, that they shall have the garden; they fight in Allah's way, so they slay and are slain; a promise which is binding on Him in the Taurat and the Injeel and the Quran; and who is more faithful to his covenant than Allah? Rejoice therefore in the pledge which you have made; and that is the mighty achievement.
Qur’an 9:123—O you who believe! fight those of the unbelievers who are near to you and let them find in you hardness; and know that Allah is with those who guard (against evil).
Qur’an 47:35—Be not weary and fainthearted, crying for peace, when ye should be uppermost: for Allah is with you, and will never put you in loss for your (good) deeds.
Qur’an 48:29—Muhammad is the Messenger of Allah, and those who are with him are severe against disbelievers, and merciful among themselves.
Sahih Muslim 33—The Messenger of Allah said: I have been commanded to fight against people till they testify that there is no god but Allah, that Muhammad is the messenger of Allah, and they establish prayer, and pay Zakat and if they do it, their blood and property are guaranteed protection on my behalf except when justified by law, and their affairs rest with Allah.