Correct me if I'm wrong, but towards the end of the bubble (2008) GS had insured (bet against) the CDOs that it had previously been propping up.
[1] https://www.huffingtonpost.com/david-fiderer/the-cdos-that-d...
[1] https://www.huffingtonpost.com/david-fiderer/the-cdos-that-d...
There's nothing wrong with being in the middle of a line of trades. The crime is when that line becomes a loop and nothing is actually changing hands at either end.