Why did the Japanese blow up Zhang?

1928, 14 In June, the Japanese Kwantung Army shot and killed Zhang, the leader of the Feng warlord, at Huanggutun Railway Station near Shenyang. Zhang was the leader of the Fengzhi warlord supported by Japanese imperialism, became the "Northeast King" who ruled the three northeastern provinces, and expanded to Shanhaiguan many times. 1in June, 927, an Guo Jun government was established in Beijing, becoming the last ruler of Beiyang government. At this time, Zhang tried to use Britain and the United States to contain Japan, such as introducing American capital in the northeast and asking the United States to build railways such as Datong (Dahushan to Tongliao) and Shenhai (Shenyang to Hailong) and Huludao port. However, Japan's demands to build Ji-Lin-Hui (Huining, North Korea) railway, open mines and set up factories for resettlement, and to prevent China from building a port in Huludao were not complied with, which caused Japan's dissatisfaction. After Tanaka came to power on April 1927, he asked Zhang Suo for railway rights and forced Zhang to solve all "unsolved cases", which aroused the anti-Japanese anger of the northeast people. On September 4th, 20,000 people demonstrated in Shenyang, shouting "Down with Tanaka Cabinet". Guan Dongjun concluded that this was caused by encouraging Zhang and hated him. 1928 In May, the Northern Expedition led by Chiang Kai-shek defeated the army, and Zhang was ready to return to Shenyang by train. Tetsutaro Muraoka, commander of Kwantung Army, intends to send someone to assassinate Zhang, but this action is not easy to cover up his guilt. So Colonel Kawamoto, a senior staff officer, planned to blow up the car and mobilized engineers to bury explosives at the intersection of Nanman Road and Jingfeng Road at Zhanghuanggutun Station.