Looks plausible! They found them "by tracing financial flows"
> The takedown follows years of intensive investigative work to map the platform’s technical architecture and identify the individuals behind it. By tracing financial flows, analysing digital forensic evidence, and working closely with partners on the ground, authorities were able to deliver a decisive blow to one of the most prolific drug markets on the dark web.
https://www.europol.europa.eu/media-press/newsroom/news/europe-wide-takedown-hits-longest-standing-dark-web-drug-market