Aggressive male guppy hurting other fish?

Can male guppies get horribly aggressive? I had two male guppies, 5 female, 8 peacock gobies, and a small upside down catfish. I recently added three platies with week. This morning noticed two platies missing chunks from their tails (a male and female) and a female platy whose side fin was severely bitten back. My smaller male guppy has also disappeared and the remaining male really likes to chase the females, maybe he killed him? Smaller guppy is always out at meal times but wasnt today. I'm not sure what else could've attacked my platies, unless they can do it to each other? But they seemed to be swimming with each other fine.

 

I've not seen males be horribly aggressive but have observed fin nipping in heavily stocked male only display tanks.

What size tank are your fish in?

 

How weird it may sound, but guppies can become aggressive. Could be a dominance thing. But it could also be that they don't have space enough that such behavior occurs.

 

It is a 36 bowfront
and I just found my small cobra guppy dead

 

Sometimes a fish will just be a jerk.. The tank looks to have enough space for the fish to me.