The following article contains an answer for the question: How does the man thought to have murdered the spy disguise himself? , can you please find it? 

At a London music hall theatre, Richard Hannay is watching a demonstration of the superlative powers of recall of "Mr. Memory" (Wylie Watson) when shots are fired. In the ensuing panic, Hannay finds himself holding a seemingly frightened Annabella Smith, who talks him into taking her back to his flat. There, she tells him that she is a spy, being chased by assassins, and that she has uncovered a plot to steal vital British military information, masterminded by a man with the top joint missing from one of his fingers. She mentions the "39 Steps", but does not explain its meaning.
Later that night Smith, fatally stabbed, bursts into Hannay's bedroom and warns him to flee. He finds a map of the Scottish Highlands clutched in her hand, showing the area around Killin, with a house or farm named "Alt-na-Shellach" circled. He sneaks out of his flat disguised as a milkman to avoid the assassins waiting outside. He then boards the Flying Scotsman express train to Scotland. He learns from a newspaper article (read by a pair of women's undergarment salesmen) that he is the target of a nationwide manhunt for Smith's murder. When he sees the police searching the train, he enters a compartment and kisses the sole occupant, Pamela, in a desperate attempt to hide his face and escape detection. She frees herself from his unwanted embrace and alerts the policemen, who stop the train on the Forth Bridge. Hannay then escapes, hiding behind the bridge's truss.

as a milkman