The Perfect Crime is a reality-altering ability that allows Mushitaro to perfectly erase any evidence of a crime. Upon activation, the ability takes the form of small, invisible creatures oozing out of his body to tamper and "erase" any potential evidence to a certain crime. He has used his ability on various criminal cases, including erasing evidence that prove Doppo Kunikida's innocence following his imprisonment after Cannibalism, evidence to the reason why Fyodor Dostoevsky let himself get caught, and evidence for the falling murder case. Once Mushitaro revokes his ability, the evidence for such crimes will soon begin to resurface. Because of its almost seamless efficiency, it can cause even a great detective like Ranpo Edogawa to get stumped to a fault due to lack or absence of evidence. As a result, Mushitaro refers to himself as the infallible detective killer.
In "erasing" evidence, Mushitaro can also utilize other resources other than releasing the invisible oozes from his body. For instance, Mushitaro, Atsushi Nakajima, and Kyōka Izumi once escaped from their pursuers by placing stolen money on their heads, upon which Mushitaro's ability kept them from appearing on surveillance cameras. He also asserts that he can erase evidence of stealing a vehicle, in which the signal from the security cameras indicating a car being stolen will vanish as well.
Though it can alter realities, it cannot change or affect people's memories in a crime scene. For example, when a person sees a particular crime unfold personally, the ability cannot erase such kind of evidence in the memory of the witness. Moreover, some evidence that the ability has once erased may be rendered partly inefficient when some of its "memory" can be extracted. For example, Ango Sakaguchi was once able to read through Mushitaro's escape plan together with Atsushi and Kyōka by reading the memory of the stolen cash they previously used to vanish from the surveillance cameras while escaping. This allowed Ango to halt their escape despite Mushitaro erasing the possible evidence that might be taken against them.
The ability is a reference to The Perfect Crime (完全犯罪, Kanzen Hanzai?), a short detective story by Mushitaro Oguri in 1933. The story is a locked-room murder case set in a village in China's hinterlands.