I completely agree with the bias aspect and think it comes down to multiple factors, not just their attractiveness (or lack thereof

).
A male suspected of sexual violence isn't hard to believe given that it's predominantly males that commit these offences. Add in to that, that he's in the police which is seen as a position of authority/power, makes it more believable. He had the opportunity to deceive and manipulate. With so much police attention on corruption and misconduct, it was an easy sell to the public.
With LL, a lot of it will come down to the fact she's a female and a nurse. Female serial killers are less common, and less likely to be immediately suspected of multiple murders. Add in that she's a nurse, those in a caring profession, while in a position of power and authority are more linked with a nurturing view rather than being seen as manipulative or deceptive. This makes it much harder for people to go against their initial impressions and bias.
The media have a lot to answer for in how they influence perception. For example, if it was ceremonial swords rather than snow white in her room, she'd be vilified. Dyed black hair, head to toe tattoo's and they'd be trying to say she was into the occult and the babies were sacrifices, just because they can.