Any person who is chanting the holy names of Krishna (Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare) in course of chanting without offenses feels some transcendental pleasure and very quickly becomes puriﬁed of all material contamination.
Bhagavat Gita 9.2,
Cleanliness is essential for making advancement in spiritual life. There are two kinds of cleanliness: external and internal. External cleanliness means taking a bath, but for internal cleanliness one has to think of Krishna always and chant Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare. This process cleans the accumulated dust of past karma from the mind.
Bhagavad Gita 13.8-12,
One need only chant the Hare Krishna mahamantra. Everyone engaged in the practice of chanting the Hare Krishna mahamantra will be completely cleansed, from the core of his heart, and be saved from the cycle of birth and death.
Srimad Bhagavatam 7.6.1,
One who chants the holy name of the Lord is immediately freed from the reactions of unlimited sins, even if he chants indirectly [to indicate something else], jokingly, for musical entertainment, or even neglectfully. This is accepted by all the learned scholars of the scriptures.
Srimad Bhagavatam 6.2.14,
Living beings who are entangled in the complicated meshes of birth and death can be freed immediately by even unconsciously chanting the holy name of Krishna, which is feared by fear personified. — Srimad Bhagavatam, 01.01.15.
Terrorist guns can kill the material body, but the Holy Name of the Lord can kill the enemies within the mind of the person.