BBM
IMO, because she recognized the person, which would make sense that it was her husband's friend. They'd only been married about 3 months, so Dana likely didn't know her husband's friends very well but wanted to be hospitable. Likely, it was common for the man to socialize there.
IMO, they were playing something a lot rougher than chess! Could her husband's friend be the person who last saw Dana at 10:00 p.m. the night she disappeared? Maybe there was evidence of who was in her apartment, or maybe Dana mentioned to her mom who was visiting, and when her husband found out who was in the apartment, he vouched that, yes, his friend was capable of killing Dana.
Sounds like a nice lady getting mixed up with some rough characters.