The man who fatally shot former Prime Minister Shinzo Abe checked YouTube when making the firearm used in the attack on Japan's longest-serving leader, investigative sources said Sunday.The sources also said Tetsuya Yamagami, 41, has stated that he tested a homemade gun at a facility connected to a religious group he harbored a grudge against. Yamagami has said his mother made a "huge donation" to the organization, which he believes Abe was associated with.The Nara prefectural police believe he was testing the weapon ahead of a planned attack. Yamagami fatally shot the 67-year-old Abe on Fr…READ FULL ARTICLE