As of now, you should not be able to get two contacts that both help with physical evidence. Nor, should you be able to get two contacts that don't help with physical evidence. So, if your first contact was one of the evidence experts (Barber, Tailor, Shoe Maker or Banker), your second contact will not be another person from that group. Conversely, if your first contact is not from that group, your second one will be.
To even things up. I'm also adjusting those detectives who already have two contacts. I'm reassigning the second contact of those of you who already have two, if they are either both evidence experts, or neither evidence experts.
Does that make sense?
The tricky thing is that to this point increasing difficulty has forced me, in fun ways, to come up with new strategies. I don't see how adding more suspects, making people clam up more, etc. will be more fun -- it'd just make things harder. So I think a new difficulty level might be helpful just so we can earn more points, but it won't really increase the fun factor. For that, probably ballistics skills or so on that apply only to a new level of difficulty would be good.
And more featured mysteries!!! (Yes, Wayne Williams Jr., I know I too need to write one ...)