I've come/I came to the conclusion that he's not mentally ill

Suppose John has committed a crime, and the police have caught and arrested him. After conducting several interrogations, it becomes clear to them that he's not in his right mind. They decide to send him to a mental facility for further medical inspection. They appoint an officer who will be responsible for this task. The officer escorts John to the clinic, where a psychiatrist informs the officer that they will need a week to determine whether John is indeed mentally ill. So, after a week passes, the officer returns, and the doctor says to him:

I've been talking to him personally, and as he's interacted with some of my colleagues, I've been closely watching him. I've come/I came to the conclusion that he's not mentally ill; he's been simulating it the whole time.

I made up the scenario, and I wrote the text that the doctor says to the officer. I wonder if either tense is possible in this context.

Does the present perfect "I've come" imply that the doctor is open to more research, and that his conclusion is not final but rather one that he's come to so far?

Does the simple past "I came" imply that the conclusion is final, and that the doctor is sure that no additional research is needed?

This is ridiculous! You wrote up all that text just to ask us about the difference between "I've come to the conclusion" and "I came to the conclusion"????
You have asked several questions about this point. Have you not learned the difference yet?

EngLearner said:

I've been talking to him personally, and as he's interacted with some of my colleagues, I've been closely watching him. I've come/I came to the conclusion that he's not mentally ill; he's been simulating it the whole time.

I made up the scenario, and I wrote the text that the doctor says to the officer. I wonder if either tense is possible in this context.

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Possible? What do you mean? How does knowing whether something is possible help you? You need to know which tense to use.

The context you've written here seems to me deliberately intended to be talking about the present. In fact, every verb (which I've put in blue) is very appropriately in present tense. So why would you then want to put one of those verbs in the past?

EngLearner said:

Does the present perfect "I've come" imply that the doctor is open to more research, and that his conclusion is not final but rather one that he's come to so far?

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No. It means he's focusing, quite rightly, on the present result. His conclusion, and the implications thereof, are relevant now, and into the future.

EngLearner said:

Does the simple past "I came" imply that the conclusion is final, and that the doctor is sure that no additional research is needed?

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No. Don't use the past tense here. It would be odd to suddenly start talking about the past. That doesn't mean it's 'impossible', however.

jutfrank said:

The context you've written here seems to me deliberately intended to be talking about the present. In fact, every verb (which I've put in blue) is very appropriately in present tense. So why would you then want to put one of those verbs in the past?

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I have the following example the style of which I copied:

The prices of stocks have skyrocketed, and so has the wealth of those who own them. Some see signs of mania. As more Americans try to get in on the party, some worry a crash is to come. As the financial world has been diverging from the real world, I've been trying to understand the many forces at play, and I found one institution has been at the center of it all - the federal reserve - the nation's central bank.

Source: "The Power Of The Fed", a documentary (timestamp: 0m57s).

The situation the narrator describes in the video is set in the present, so he uses the present tense accordingly (the blue bolded verbs). However, he then, out of the blue, says "I found" instead of "I've found". Does the simple past "I found" sound right here?

EngLearner said:

However, he then, out of the blue, says "I found" instead of "I've found". Does the simple past "I found" sound right here?

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There is a contextual reason the speaker shifts to the past there. I can't watch the video but I'll guess that it's to focus on what's to come in the documentary—i.e., we're going to go back in time and watch him or her do the finding. In other words, there's a link from the introduction to the main part of documentary, which is set in the past.

As I say, that's just a guess. If you've watched the doc and can see the context, could you tell me if I'm right?

jutfrank said:

As I say, that's just a guess. If you've watched the doc and can see the context, could you tell me if I'm right?

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Later in the video, he engages in conversation with diverse individuals, extracting information to demonstrate to viewers how he reached the conclusion he initially presented. However, all these conversations appear to be recent, occurring in the period leading up to the present.