A non-starter.
The American government doesn't go easy on spies from any country. Witness the continued incarceration of Pollard. He's right where he belongs.
Were they selling art? Did they have fake green cards and visas? Were they deported? Is the DEA memo a fraud?
Something sure seems to have occurred. The mainstream "liberal" media you mention has not reported this except the Washington Post which ran a vague government denial. This has been carried by the Jewish publication The Forward, FOX NEWS, the Washington Times, Le Monde, Insight Magazine and Jane's Intelligence Review. If there wasn't anything to this , it is doubtful they would have reported it at all.