JMO, I'm of the opinion that con artists are capable of much more than just conning people financially. It's not just AT and BB that makes me believe this.
I knew someone years ago (not a friend of mine) who was a con artist from the time he was a little kid. His "thing" was to find a target, gain their trust and then steal from them. He had many victims and was in and out of trouble with the law for years for financial crimes against others.
His last crime was kidnapping and attempted murder and he's now in prison with LWOP. No one could believe he was capable of doing what he did. Everyone thought he was "just" a con artist.
Believe it, IMO. It's not normal to prey on others, to gain their trust through deception and then commit a crime against them. I believe mental health professionals would say this is antisocial behavior.
AT has a long history of con artistry. I'm not sure if BB became a con artist after she met AT or before, but she has been convicted of a crime she committed with AT involving a scam with gold coins and IMO, she conned Sydney into thinking she was real.
Was Sydney their first victim? IDK, but the two videos they made and published on facebook after Sydney was murdered, but was still missing, showed that neither of them had any conscience or remorse about what they had done, and they lied about having nothing to do with Sydney's disappearance. There was no empathy for Sydney, her family or her friends.
Hideous creatures, IMO.