Lawyer Eri Kisaki's Testimony (Part 1) Meitantei Conan : Season 17 Episode 15

Eri goes to a hairdresser to get her hair done. Conan and the others come across a dead body outside. Conan finds the woman who did Eri's hair to be the killer, but with Eri as her alibi, it makes it difficult to prove she did it. What was the trick used in order to carry out the crime?