I am sorry but all the replies to the 3 cases were wrong.I wanted to tell you that in the pen case conan and mouri kogoro are about to go somewhere by train ,i guess.But after some time they witness two men fighting,and one pushes the other and dies,i guess.Conan cathes the assailant by telling the police that the culprit had the victim's pen.
And in the male friend murder case,i am asking about the case which was more than 2 episodes.The male friend committed the crimes because of his wife's death.