If police are focusing their investigation on you, you absolutely should not talk to them for any reason whatsoever. Even if you are not arrested, your statements may be used against you even without any Miranda advisement because you have not yet been arrested.
You should immediately contact an experienced criminal defense attorney to protect you.
No attorney-client relationship is established between this lawyer and the originator of the question. This answer is provided for informational purposes only and is provided purely to assist the questioner in determining whether to consult with an attorney to obtain legal advice specific to their matter.
You need a lawyer on your side. Talk to a good criminal defense attorney before you talk to the police again.
This response does not create an attorney client relationship and is offered for informational purposes only. Only a lawyer fully versed on the facts and circumstances of your case can properly advise you on the case. I am licensed to practice in Minnesota, not every state. You should always consult with an attorney licensed in your area on how best to proceed.
In the question you asked you noted that you were the last person to see a murder victim and now "you are a suspect." If that is true or one has a reasonable belief he is a suspect of a crime, and/or there is a pending investigation by law enforcement, you should immediately seek advice from a criminal defense lawyer.
I do not know a single criminal attorney who would permit his client to be "interviewed" by law enforcement under the circumstances you describe because it would more likely constitute an INTERROGATION. This is not a format for discussion.
Not only could anything you say be used against you unless you were advised of your right to first speak with a lawyer (the Miranda warnings that must be made by the police or sheriffs), it is possible you might make inconsistent statements as well. There is no requirement for you to participate in an alleged "interview" as any such discussion would more likely be lengthy and at some point you might make statements you later wished you had not, only falling victim to the abusive techniques that have in some cases led to admissions or a confession for individuals who just want to end the confrontation and examination.
Regardless, you need to retain an experienced criminal defense attorney NOW. It is not your job to "get this sorted out" and/or to "make them believe me" as you seem to desire. It is understandable that you want to help find the person who killed your friend, but this is not the way.
Again, you should retain legal counsel before doing anything else.
Sometimes you are not even really a suspect. They are just trying to scare you. Just because you were the last person to see someone doesn't mean anything. All it means is that after you saw them, someone else may have killed them.
They probably want you for questioning to try and interrogate you and coerce you into making a false confession or making a statement that would incriminate yourself.
My advise to you, is do not go about this on your own. This is a serious crime (most serious) and the police detectives are trained to trick you into answering their questions.
Remain silent, because you have a right to and invoke your right to an attorney.
You absolutely cannot and must not speak to detectives or anyone for that matter without a lawyer present. You should also not post your comments here. Obviously this is the most serious criminal case you can be involved in. You should hire counsel now to assist you and not speak to anyone. You should consult with a lawyer immediately. We would be happy to give you a free consult.