CoStar Group, Inc. v. Commercial Real Estate Exchange Inc., 2:20-cv-08819

The case involves allegations that CREXi engaged in mass copyright infringement by systematically accessing LoopNet (owned by CoStar) to copy images, which were then posted on CREXi’s platform.
CoStar hired digital forensics expert Roffman to analyze LoopNet activity logs and attribute activity to CREXi using IP addresses and other technical methods.
CREXi filed a motion to exclude Roffman's expert testimony under Federal Rules of Evidence 403 and 702, arguing it was more prejudicial than probative and methodologically unreliable.
Roffman's analysis relied on various indicators found in web session data, including IP addresses and patterns of VPN/BPO use, to associate over 8 million LoopNet website “hits” with CREXi or its agents.
The legal issue concerned whether Roffman’s testimony was admissible given challenges about its reliability and risk of unfair prejudice, particularly now that some of CoStar’s other claims had been abandoned.
The court was asked to resolve whether the expert testimony should be limited or excluded before trial.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Admissibility under Rule 403 (prejudice)	Evidence is highly relevant to theory of mass infringement	Testimony is minimally probative, unfairly prejudicial, will confuse or mislead jury	Prejudice did not substantially outweigh probative value; testimony admitted
Admissibility under Rule 702 (reliability)	Roffman used reliable forensics methods in context of case	Use of IP addresses is unreliable to attribute activity to CREXi	Methodology was adequately explained; reliability challenges go to weight, not admissibility
Relevance of volume of activity	Relevant due to mass scale infringement theory	Volume is irrelevant after misappropriation claim dropped	Volume of activity relevant to remaining copyright claims
Inclusion of sessions/IPs with no clear indicator	Capture all possible CREXi-related activity, explained methodology and over-inclusiveness	Over-inclusive; attributes too much activity to CREXi	Methods sound; concerns appropriate for cross-examination

Kumho Tire Co. v. Carmichael, 526 U.S. 137 (U.S. 1999) (Daubert factors apply flexibly to expert testimony)
Daubert v. Merrell Dow Pharm., Inc., 43 F.3d 1311 (9th Cir. 1995) (focus is on soundness of methodology, not correctness of conclusions)
Primiano v. Cook, 598 F.3d 558 (9th Cir. 2010) (court decides reliability, jury decides weight)
City of Pomona v. SQM N. Am. Corp., 750 F.3d 1036 (9th Cir. 2014) (reliability inquiry is flexible, challenges beyond threshold are for the jury)