I have a 20 gallon tank with a Marineland 150 Biowheel filter and both live (Amazon Broad & Anarcharis) and artificial decoration that has been set up for about 2 months and has finished cycling. The tank currently has:

-3 Mickey Mouse Platies
-4 Lyretail Dalmatian Mollies (3 female, 1 male)
-2 Neon Tetras (was 5, see below)

About 72 hours ago, I had 5 Neon Tetras. Over the course of the next 24-36 hours, two of them turned up dead, but I didn't know why. Then, last night, I saw a female Dalmatian Molly attacking and killing one of the Neon Tetras (it wasn't very fun to watch, but I couldn't do anything to help him and didn't have a QT tank). I've noticed that this same Molly has also been very aggressive towards another female in the tank. I was careful in selecting my fish to make sure they were likely to get along and was sure the schooling Neons, while smaller, would do well with the communal livebearing Mollies and Platies.

Can anyone tell me why the female Molly (and yes, I'm certain she is a female) is attacking my Tetras and other Mollies? Is it some sort of mating thing? If I removed the male from the tank, would it make a difference? Was I wrong about the compatibility of Neon Tetras and Mollies?