1x7 - Detective Conan: Shinichi Kudo's Written Challenge

After attending the funeral of a famous ramen chain owner, Sonoko gets kidnapped along with Yuri Noguchi! Miki, Yuri's sister, receives a phone call from the kidnapper demanding a large amount of money in diamonds. Shinichi and Ran manage to get to Sonoko and Yuri safely, only to find Miki was murdered when she was separated from them! Who killed Miki and why?