Concerns are rising over the potential spread of copycat crimes after a man in his 60s who killed his son with a homemade gun in Incheon stated that he learned how to make the weapon through YouTube.

Gary Johnson, 58, was arrested by Lodi Police on Feb. 6 on suspicion of a firearm offense. Officers allegedly found a “homemade” firearm in his possession that was capable of firing 12-gauge shotgun ...