Can I contact this person, obtain a statement of facts, and submit the signed statement to the court, or my attorney?
Can you contact him? Your post seems to indicate you can. However, I doubt that's what you intended to ask. First, and most importantly, you don't submit witness statements to the court. If you want the witness to testify at trial, you/your lawyer needs to subpoena him; a written statement won't be admissible. Second, even if it were admissible, it would be a terrible idea for you to obtain it. You're obviously biased, so why would anyone believe the statement accurately reflects what the witness told you? You could even run the risk of being accused of tampering with the witness. Also, anything you say to the witness would be admissible if the prosecutor wanted to call the witness to the stand.
Or does the statement need to be submitted in court through an investigator?
A statement obtained by a PI would be used by your attorney to determine whether or not to call this person as a witness or for other things, but, as explained above, it would not be submitted to the court. If your attorney wants to file a pretrial motion, the witness would need to sign a sworn affidavit.
If your wondering why I do not ask my attorney this question? He has got angry at questions I asked before
Who cares if he gets angry? It's your ass on the line, not his.