The thief stealing company technology was actually Kazuomi Isshiki. He was selling the components to Hiraguchi, an R&D employee at Myojo Technics, for a profit. The mouse robot created by Takeshi Tanizaki was actually designed as a security device to help him catch the person stealing company secrets. It was tuned to spray and detect traces of a special ink (of a type which Isshiki kept at home, and which got stuck on his shoes) the culprit left at the scene of his thefts. Tanizaki met in secret with Makita, an HR employee at Myojo Technics, in order to find out the dates of their newest presentations, thus learning when the thief would strike next.
Upon catching Isshiki in the act, Tanizaki attacked the thief but was wounded in the process. As Isshiki attempted to escape, his rope came undone when the gas pipe he had tied it on broke because he had repeatedly used it to vault down the window every time he broke in, and he began to fall. Tanizaki grabbed the rope in an attempt to save the culprit's life, but the strain was too much and he started to lose strength causing the rope to latch around his neck killing him, which Isshiki failed to notice. This was proven because there was traces of rust on the back Tanizaki’s jacket and his blood on the vent because he had hit his head when the rope had patched around his neck. Isshiki breaks down in tears once he realized that his actions lead to Tanizaki's death.