In that case he cannot have been the murderer

"In that case he cannot have been the murderer," said the detective quickly, "because the shots were fired while he was still in the room. They were almost simultaneous with the appearance of the flash at the upper window."
"H'm!" said Saul Arthur Mann, for the moment nonplussed.
"The more you go into this matter, the more complicated does it become," said the police officer, with a shake of his head, "and to my mind the clearer is the case against Merrill."
"With this reservation," interrupted the other, "that you have to account for the movements of Mr. Rex Holland, who comes on the scene ten minutes after Frank Merrill arrives and who leaves his car. He leaves his car for a very excellent reason," he went on. "Sergeant Smith, who runs away to get assistance, meets two men of the Sussex constabulary, hurrying in response to Wiseman's whistle. One of them stands by the car, and the other comes into the house. It was, therefore, impossible for the murderer to make use of the car. Here is another point I would have you explain."
He had hoisted himself on the edge of his desk, and sat, an amusing little figure, his legs swinging a foot from the ground.
"The revolver used was a big Webley, not an easy thing to carry or conceal about your person, and undoubtedly brought to the scene of the crime by the man in the car. You will say that Merrill, who wore an overcoat, might have easily brought it in his pocket; but the absolute proof that that could not have been the case is that on his arrival by train from London, Mr. Merrill lost his ticket and very carefully searched himself, a railway inspector assisting, to discover the bit of pasteboard. He turned out everything he had in his pocket in the inspector's presence, and his overcoat--the only place where he could have concealed such a heavy weapon--was searched by the inspector himself."
The detective nodded.
"It is a very difficult case," he agreed, "and one in which I've no great heart; for, to be absolutely honest, my views are that while it might have been Merrill, the balance of proof is that it was not. That is, of course, my unofficial view, and I shall work pretty hard to secure a conviction."
"I am sure you will," said Mr. Mann heartily.
"Must the case go into the court?" asked the girl anxiously.
"There is no other way for it," replied the officer. "You see, we have arrested him, and unless something turns up the magistrate must commit him for trial on the evidence we have secured."
"Poor Frank!" she said softly.
"It is rough on him, if he is innocent," agreed Nash, "but it is lucky for him if he's guilty. My experience of crime and criminals is that it is generally the obvious man who commits that crime; only once in fifty years is he innocent, whether he is acquitted or whether he is found guilty."
He offered his hand to Mr. Mann.
"I'll be getting along now, sir," he said. "The commissioner asked me to give you all the assistance I possibly could, and I hope I have done so."
"What are you doing in the case of Jasper Cole?" asked Mann quickly.
The detective smiled.