I don't think you should just label him a murderer just yet. I had a bichir in the tank with my jardini and they got along fine, they were both about the same size tho (the bichir a bit longer). That is until the bichir jumped out of the tank and committed suicide one night while I was sleeping...so I'm not sure if the jardini was the one that made him jump. Anyways, I think that since your aro is still relatively small, you should try either bichirs, datnoids, or clownknives at least the same size as your aro and hopefully they can grow old together. I'm having problems finding a large tiger datnoid since my aro has grown to 8"-9" now.