Experts are expensive. Is hiring one a necessary expense for social media evidence?
Questions of admissibility are up to the trial judge, and in most jurisdictions, the appellate courts review the decisions on an abuse of discretion standard. Translation: I hope this post is helpful, but ultimately, the judge has the say on what's required to authenticate evidence and show it to the jury.
The threshold issue in determining if an expert is needed is whether the evidence requires scientific, technical or other specialized knowledge to understand. You may recognize that from good ol' Federal Rule of Evidence 702, or the Daubert standard.
Given the near ubiquity of social media, it doesn't seem likely that there are many jurors (or judges if you're in a bench trial) who aren't familiar with the likes of Facebook, Twitter, Instagram, LinkedIn and Pintrest. FYI - there's way more social networking out there.
Anyway, if all we're talking about is authentication and chain of custody, then I do not think you need to run out and find a software engineer, computer expert or digital forensic expert to testify about how he found the Facebook post, printed it, and then ever-so-carefully walked it to the courthouse so the fine jurors could review it. No, considering that most 4-year olds can perform that task, I don't think we need a post-doctoral candidate's expert opinion.
But lawyers being lawyers (and judges being judges), it's always better if you have some precedent to prove your point. May I suggest State v. Taylor, 178 N.C. App. 395, 632 S.E.2d 218 (N.C. App. 2006). Mr. Taylor was found guilty of first degree murder, first degree kidnapping and robbery. He appealed on several grounds, including the trial judge's admission of text message transcripts over Mr. Taylor's motion in limine; more specifically, Mr. Taylor argued that the text messages were not properly authenticated.
The prosecution authenticated the text messages by having a Nextel store manager testify that he downloaded the content of the texts from Nextel's website, printed them off, and then "ever-so-carefully walked it to the courthouse so the fine jurors could review it." No, that is not in the opinion. I'm quoting myself.
The North Carolina Court of Appeals found this to be sufficient and declined to reverse his conviction on these grounds. Key to the Court of Appeals decision was Rule 901(b)(1) of the North Carolina Rules of Evidence. Rule 901 provides a non-exhaustive list of ways to authenticate evidence. Subsection (b)(1) allows a witness with knowledge "that a matter is what is claimed to be" to authenticate something.
The Court of Appeals also held that there need not be direct evidence that the person wrote the post as long as there is other circumstantial evidence form which the jury could infer authorship: Rule 901(b)(4) provides authentication may be made through "[a]ppearance, contents, substance, internal patterns or other distinctive characteristics, taken in conjunction with circumstances."
The jump to social media posts is quite easy, especially since the store manager in Taylor printed off the information from a website. As long as the witness can testify that he saw the post and there is other circumstantial evidence (say a photo of the person), then there is probably no need to hire an expert to perform this otherwise mundane task.