I have an aggressive fish and I'm not sure which one

My girlfriend and I have a 100 gallon tank with a number of fish (inherited with the tank, we have not purchased any since acquisition), and for several months it's been great. However in the last week we've lost 3 fish to injuries and we can't figure out which fish could be the culprit.

We have:

• 2 candy cane tetras
• 5 cardinal tetras
• 7 neon tetras
• 8 rummy-nose tetras
• 3 black neon tetras
• at least 10 kubotai
• 1 dwarf gourami
• 5 kuhli loaches
• 1 very large mystery snail

We haven't had any issues before, and the people who had the tank before us never had any issues. We change the water weekly and when we check the water the levels are always in excellent condition. We've lost a neon tetra, a kubotai, and a black neon tetra all to injuries (it looks like they were eaten partially) and we are desperate to figure out which fish it could be and why this is suddenly happening. We thought they were just dying at first and that the other fish were eating the corpse, but then we saw one with a bite out of it while still alive and it died the next day, and another was very obviously attacked and had serious injuries (we had to mercy it because it started corkscrewing).

Can anyone help us figure out what's wrong? I hate knowing that they are either unhappy or in danger, and I'd really like to not have another fish funeral any time soon.

Also to note: we have a secondary 10 gallon tank that we have to eventually use as a quarantine tank. It also has great tank conditions. We've been using it as a "triage" space, separating the injured fish from the main tank to prevent additional injuries and to also prevent a possible death in the main tank.