Here's the crux of their reasoning & requested information in seeking the warrant, from the linked PDF:
As discussed above, Earnest made a posting in which he thought to draw attention to his forthcoming attack on the Chabad of Poway, share his views through his open letter, and offer people the opportunity to observe the attack itself. Several people responded, both individuals who were taken aback about the posting as well as people who were sympathizers. As a result, some of the individuals may be potential witnesses, co-conspirators and/ or individuals who are inspired by the subject posting. Based on agents' training and experience, following attacks such as those conducted by Earnest, other individuals are inspired by the attacks and may act of their own accord. For example, as described above, Earnest himself was inspired by the Christchurch event in New Zealand.
Regardless of the nature of the comments, the evidence sought to be seized as described in Attachment B is relevant as evidence of Earnest's bias and motivation in committing the hate crimes set forth in Attachment B. Even comments made in response to the subject posting or about it are relevant to Earnest's motivation for his violent attacks to the extent that as explained above, some of the posters may be potential witnesses, co-conspirators and/or individuals who are inspired by the subject posting. As discussed above, Earnest stated in the subject posting, "I've only been lurking for a year and a half, yet, what I've learned here is priceless." This information suggests that Earnest was inspired and/or educated by individuals who commented on his threads.
Based on this information, there is reasonable cause to believe that the information sought, specifically IP address and metadata for all commenters, constitute evidence of his motivation in committing the offenses described herein and are thus relevant and material to an ongoing criminal investigation, information that may be sought by an order issued pursuant to l S U.S.C. § 2703(c) and (d). That is, the information may lead to the identity of individuals who inspired and/or educated Earnest or are aware of his motivation in committing the attacks.
>...and/ or individuals who are inspired by the subject posting
That's a very overarching goal as it would, in theory, require continued surveillance of all subjects to determine inspiration - either in the past, present, or even the future, yeah?
I mean, you can't just take a snapshot of time,
time_t now = time(0);
tm *gmtm = gmtime(&now);
and consider that no other people would be "inspired" in the future by this event, yeah?
There should be more discussion about the ridiculously broad nature of this warrant... How are they able to say anyone who commented at all is a potential co-conspirator?
They should be required to have a more clear guideline than someone who just commented. It's basically a drag net.
As discussed above, Earnest made a posting in which he thought to draw attention to his forthcoming attack on the Chabad of Poway, share his views through his open letter, and offer people the opportunity to observe the attack itself. Several people responded, both individuals who were taken aback about the posting as well as people who were sympathizers. As a result, some of the individuals may be potential witnesses, co-conspirators and/ or individuals who are inspired by the subject posting. Based on agents' training and experience, following attacks such as those conducted by Earnest, other individuals are inspired by the attacks and may act of their own accord. For example, as described above, Earnest himself was inspired by the Christchurch event in New Zealand.
Regardless of the nature of the comments, the evidence sought to be seized as described in Attachment B is relevant as evidence of Earnest's bias and motivation in committing the hate crimes set forth in Attachment B. Even comments made in response to the subject posting or about it are relevant to Earnest's motivation for his violent attacks to the extent that as explained above, some of the posters may be potential witnesses, co-conspirators and/or individuals who are inspired by the subject posting. As discussed above, Earnest stated in the subject posting, "I've only been lurking for a year and a half, yet, what I've learned here is priceless." This information suggests that Earnest was inspired and/or educated by individuals who commented on his threads.
Based on this information, there is reasonable cause to believe that the information sought, specifically IP address and metadata for all commenters, constitute evidence of his motivation in committing the offenses described herein and are thus relevant and material to an ongoing criminal investigation, information that may be sought by an order issued pursuant to l S U.S.C. § 2703(c) and (d). That is, the information may lead to the identity of individuals who inspired and/or educated Earnest or are aware of his motivation in committing the attacks.