He used to make deals with Kate Freelander, and lured her brother Thad into gambling with him in order to get to Kate again after she had joined the Sanctuary Network. He wanted to use her in order to obtain abnormals, but she refused.
In order to get what he wanted, Constantine had Thad abducted and blackmailed Kate to get him into the Sanctuary and steal an abnormal. However, Kate instead opened the Sorkel's cage when Constantine was standing in front of it. The abnormal grabbed, killed, and devoured him.