There is no leaked screenshot. It is an affidavit filed as part of an indictment. You can read it here on this government website:
https://www.justice.gov/usao-edca/file/836576/download.
Furthermore, the affidavit does not relate at all to "illegal or suspicious activities on the blockchain". The evidence was found primarily by looking at records found on Silk Road servers.
As for the task force, it seems fairly mundane:
I am part of a digital currency task force focused on identifying the use of digital currency to launder the proceeds of criminal activity. As part of this task force, I have been involved in several investigations into unlicensed digital currency exchangers and narcotics distributors on the darkweb who use digital currency to receive payment for the sale of narcotics.