We identify a lens primarily by looking at the spectrums and redshifts of the lensed object.  If they are nearly identical then there is a good chance that it is a lensed system. So, this system has been identified as a lensed system, but unlike typical systems, deep ccd imaging and radio imaging have both failed to reveal the source.  Estimating the parameters of the system, we should be seeing an object with a mass of 10^13 Mo in between the images.