Trying to learn to write in english 7

I was staying outside all alone., thinking about all this, about that guy and the letter. Why did he kill her and why he has has he this letter. ? A thought came to me that probably her sister was dead as well. But what if not? The old man said she had hurried when he saw her on at the station and I supossed she hurried to Manchester to her sister. There must have been two reasons. (I think you mean maybe 'there must have been one of two reasons' - or 'there could have been two possible reasons') The first is that she was told that with her sister had happened terrible things had happened to her sister or the second is that she learned something about herself and her sister. Anyway, I should wait for the police and make a suggestion I have tell them what I think. If I tell them about letter it will help them a lot with investigation and they will make sure Elizabeth will be safe. If it is not too late. I went back to the train and sat next to the old man. I swear he looked like he just lost a daughter. He was very king (a very kind??) person, I guess. We were patiently waiting for the police and ambulance.

'...and make a suggestion I have' is good English, but it means you will be telling the police something you think they should do - I think you mean you will give them your information and ideas.

Well done - very good English