People expect a positive investigation result. Asking yourself, what kind of evidence would be "enough" to say it is not a lab leak? This is not obvious. Any negative result would beg deeper questions on trustworthiness of the given data, thoroughness of the research in this manner etc.
No negative investigation result is acceptable to the public IMHO.
Even if it were true that "the public" would not accept an acquittal at trial (although they sure were quick to accept acquittal without a trial), what does that have to do with scientific investigation? If there were reasonable candidate ancestors for SARS-COV2 found in nature, it would support natural origin, and be "enough" for many current skeptics. The weight of evidence is currently in support of lab leak, regardless of opinion one way or the other.
No negative investigation result is acceptable to the public IMHO.