Trying to learn to write in English 8

The police and an ambulance appeared almost simultaneously. A few policemen were inspecting the body while the others were questioning people who had been in that train at the time a murder had occured. There was a lot of people. It seemed like a regular crime scene, I supposed. One of the policemen came to me, and asked if I was all right, and said that he had to questioned me. I told him the whole story including the very beginning, about that guy and how he was acting himself in a highly suspicious way [could also say just 'suspiciously' or 'very suspiciously']. I described him in detail. Afterwards, I said that I had found something when I had tried to catch him. "What would I have done if I had succeeded. I can't imagine I could have seized ['grabbed' or 'caught' sound more natural] him or something." I think. [Not sure what is meant by this; maybe that period shouldn't be there?] I said that he could be some kind of a serial killer and there might be another victim, her sister. I think he treated [maybe 'He seemed to treat'] my theory with scepticism, but he sent for a detective.