Marsh's primary field is actually psychopathy research. You can see her lab's cv here a lot of the papers are there too, all PDFs though. A number of their paper's deal with the same genotype, the most obviously relevant one to your concern is a finding that s-carries experience fear-recognition impairment following tryptophan depletion. A google search for the 5-HTTLPR and psychopathy returns a mixed bag- it looks like the short allele might be a risk factor for ASPD which correlates with the psychopathy checklist. But it looks like there is a gene-environment interaction happening.

Depressingly, someone may have actually tested more directly for a correlation and it just got buried as a negative result.