Hillary Clinton adviser Huma Abedin, right, at the third presidential debate on Oct. 19. (Drew Angerer/Getty Images)

FBI Director James B. Comey recently announced that the FBI had discovered new emails that might be relevant to the investigation of Hillary Clinton’s email server. The emails were discovered in an unrelated case, and the FBI now plans to search through the emails as part of the Clinton server investigation.

Comey’s announcement raises an important legal question: Does expanding the FBI’s investigation from the unrelated case to the Clinton case violate the Fourth Amendment?

We don’t know all the facts yet, so it’s somewhat hard to say. But here’s why the expansion of the investigation might be constitutionally problematic. Consider this a tentative analysis unless and until more facts emerge.

From what I can patch together, the FBI was investigating former congressman Anthony Weiner for potential crimes involving sexting with an underage girl. As part of the investigation, the FBI seized Weiner’s laptop to search it for evidence of the sexting crimes. I would guess, although I haven’t yet been able to confirm, that the FBI obtained a warrant to search Weiner’s computer. The Fourth Amendment would generally require a warrant to search a suspect’s personal computer unless there are special circumstances such as consent that haven’t been mentioned in press reports.

The case connects to Clinton because the laptop happens to have been shared by Weiner and his now-estranged wife, Huma Abedin, who is an important adviser to Hillary Clinton. [UDPATE: Abedin has since stated that the computer only belonged to Weiner, and that she did not use it.] In the course of searching Weiner’s laptop, the FBI came across emails in Abedin’s email account that appeared to the agents to be relevant to the Clinton email server case. According to news reports, the FBI now is planning to get a warrant to search the laptop for emails related to the Clinton server case. They haven’t obtained that warrant yet, however, so the Weiner computer has not yet been subject to a comprehensive search.

Former Rep. Anthony Weiner (D-N.Y.) has repeatedly been exposed for sending lewd messages and photos to women online. Here's a definitive guide to his sexting scandal. (Peter Stevenson/The Washington Post)

If these facts so far are accurate, the FBI may have violated the Fourth Amendment in expanding the investigation from Weiner to Clinton. Here’s the problem. If the FBI was searching Weiner’s computer, it presumably had a warrant authorizing the search of the computer only for Weiner’s communications with underage girls. If that is correct, going from that narrow search to a broader search of Clinton’s emails raises two potential problems for the FBI.

The first issue is whether the FBI was permitted to search through Abedin’s email account for records of Weiner’s illegal messages with underage girls. In People v. Herrera, 357 P.3d 1227 (Colo. 2015), the Colorado Supreme Court provided some reason to think that the answer may be “no.” In Herrera, the government had a warrant authorizing the search of a cellphone for messages between the defendant and an undercover officer who had posed as a underage girl. When the police executed the warrant, the officers also searched a folder that contained messages between the defendant and a different (real) underage girl. The court held that searching the folder violated the Fourth Amendment because the only evidence authorized to be seized in the warrant — the messages between the defendant and the undercover officer — weren’t likely to be in the folder containing messages between the defendant and the other girl. I have criticized that reasoning, but it raises questions about whether the FBI could look through Abedin’s account for Weiner’s illegal emails.

There might be similar problems because the alleged Weiner texting crimes apparently occurred in 2016. I gather that the Clinton emails were from her time as secretary of state, which was several years earlier from 2009 to 2013. If I’m right that there was a several-year gap between the warrant crime and the second investigation, it’s not clear the government could search through older emails for evidence of such a recent crime. See Wheeler v. State, 135 A.3d 282 (Del. 2016) (holding that the Fourth Amendment was violated when a warrant to search computers for witness tampering that occurred in 2013 did not include a date restriction on how far back the search could extend; evidence of crime from a computer not used since 2012 suppressed as a result).

A second issue is whether the FBI was permitted to seize the Abedin emails, which were outside the scope of the warrant, and to use them to reopen the investigation into Clinton’s email server. I think this is the bigger legal issue for the FBI. Most courts have treated this as a matter of the “plain view” exception. If the government is searching a computer, and it comes across files that are outside its warrant but are clear evidence of second unrelated crime, the usual government practice is to take those files and use them to get a second warrant to search the computer for the second crime. That’s what the FBI appears to be doing here. They are getting a second warrant after discovering Abedin’s emails because what was likely a first warrant for Weiner’s emails wouldn’t justify the second and broader search. See, e.g., United States v. Carey, 172 F.3d 1268 (10th Cir. 1999).

But if that’s true, there’s a problem: The plain view exception does not allow evidence to be seized outside a warrant unless it is “immediately apparent” upon viewing it that it is evidence of another crime. Just looking quickly at the new evidence, there needs to be probable cause that it is evidence of a second crime to justify its seizure, which would presumably be necessary to apply for the second warrant. See Arizona v. Hicks, 480 U.S. 321 (1987); United States v. Williams, 592 F. 3d 511, 522 (4th Cir. 2010).

Democratic candidate Hillary Clinton's private email server was once again pushed into the lime light when FBI Director James B. Comey announced that he would resume looking into the case with less than two weeks before the election. The development has left the campaign scrambling to head off the potentially game-changing damage. (Alice Li/The Washington Post)

But it’s not clear how that would be the case here. Comey’s letter to Congress is really tentative. It says that the FBI has discovered emails that “appear to be pertinent” to the Clinton investigation. Comey then says that the FBI should take “appropriate investigative steps designed to allow investigators to review these emails to determine whether they contain classified information, as well as to assess their importance to our investigation.” One report says that the FBI has “no idea” about the content of the emails.

The Fourth Amendment plain view standard doesn’t allow a seizure of emails based on a mere we-hope-to-later-determine standard. The government can’t seize the emails just because the Clinton investigation is extra important and any possible evidence is worth considering. Rather, the Fourth Amendment requires the initial look at the emails to generate “immediate” probable cause that they are evidence of a crime first, before their seizure is permitted and used to get a second warrant.

Was the plain view discovery sufficiently clear and illuminating that it gave the FBI that probable cause? We don’t yet know.

I should add that the scope of the plain view doctrine for computer searches is very much in flux, which adds some uncertainty to this issue. For example, the FBI might argue that using the discovery of the Clinton emails to apply for a second warrant was permitted by the first warrant and is not an additional “seizure” and therefore does not need to be justified. By that reasoning, the FBI is free to scour Weiner’s laptop for evidence of any other crimes for as long as it wants, and to take its time to see if there is enough evidence to justify a second warrant.

I think that’s a somewhat hard argument to make in light of the plain view cases such as Carey and Williams, but it’s at least possible. I should also add that some courts and scholars, myself included, have suggested that the plain view doctrine should be narrowed or even eliminated in computer search cases. Under that reasoning, expanding the search becomes more clearly problematic. See this recent article for more on my views.

I should also flag the question of whose rights are at issue, which determined who would have standing to enforce their rights. The computer was used by Weiner and Abedin, which means that it’s only their Fourth Amendment rights, not Clinton’s or other staffers’, that are potentially at stake. Hypothetically, if the FBI violated the Fourth Amendment in the course of getting to the Clinton emails, and the emails end up revealing crimes involving Clinton staffers and Clinton, the only Clinton person who could move to suppress the evidence would be Abedin.

As I noted at the beginning, this a tentative analysis unless and until more facts emerge. My apologies if I missed some relevant facts that have already been disclosed. I looked around, but in my haste to get out a post I very well might have missed something. I’ll probably be pretty busy Sunday, but I’ll try to update the post if necessary if I missed something big — thanks in advance for your patience.