From that domain Is This Legal?

Here at NegativeSEO.me we only use legal means to ensure your competitors get banned. Google will penalize a site for bad links. If we create bad links to your competition, we can get them banned on google, while staying completely in the framework of US legislation.

I would get multiple law firms involved in this one.

A civil lawsuit is a remedy for dispute. It's about "money". You forced me through unfair business practices to lose money and your client received unjust enrichment through those acts.

No one needs to prove you did something illegal. Violating multiple services TOS will do nicely.

There were suggestions of false DMCA claims which falls under copyright law.

§ 506. Criminal offenses⁴

(a) Criminal Infringement. —

(1) In general. — Any person who willfully infringes a copyright shall be punished as provided under section 2319 of title 18, if the infringement was committed —

(A) for purposes of commercial advantage or private financial gain;

(B) by the reproduction or distribution, including by electronic means, during any 180-day period, of 1 or more copies or phonorecords of 1 or more copyrighted works, which have a total retail value of more than $1,000; or

(C) by the distribution of a work being prepared for commercial distribution, by making it available on a computer network accessible to members of the public, if such person knew or should have known that the work was intended for commercial distribution.