The case for the defence

This story is written by Grahame Greene. He wrote novels, short stories, plays and travel books.
This is a crime story in which we don't know who the murderer is.

An old woman was found battered to death at two o'clock in the morning. A man was taken into custody. There was a witness, Mrs Salmon. She had been unable to sleep she had seen Mr Adams in Mrs Parkers garden with a hammer. It was dark but the street lamp exposed him. There were other witnesses too but she was the ideal witness. In court the counsel asked Mrs Salmon to look at another man. This was Mr Adams twin brother. After that there wasn't a witness prepared to swear that Mr Adam was the man they had seen. After the hearing, when the twins were leaving, one of the twins got pushed on to the road right in front of a bus. His skull smashed just as Mrs Parkers had been. Is the murderer dead or is an innocent man dead?