This killer is leaving a lot of psychological evidence behind.
Head and front legs cut off. Head dumped together with body, front legs missing.
This seems like an obvious expression of power and perhaps anger? According to this report, killing like took place in the wee hours of Tuesday. Cats are nocturnal. Cat singing pissed him/her off? Too noisy? Couldn't sleep/study? Babies stressing you out? Had a bad Monday at work? Or the cat simply rejected your attempts to pet it?
Killer targets smaller, weaker animals likely due to the lack of power and authority in daily life. Maybe he/she is constantly getting ordered around, scolded or bullied by others, frequently getting frustrated at work and yet being unable to do anything about it. Feels like shi t right? By targetting weaker victims, he/she gains some satisfaction and the feeling of empowerment and an adrenaline rush. This is addictive. Killer might have done similar acts to other small animals in the past. When the sense of empowerment wears off, he/she might have to renew the feeling. He/She might be killing small animals now but could likely devolve to human victims when it just wouldn't do satisfy anymore. Starting with little kids/babies. Yes. But killer did not take the trophy head. No. Too gross and scary and bloody? Risk of someone else finding the gross thing in his/her possession?
Didn't seem like there was much struggle with all the clean cuts. Report says cat could have been dead beforehand. Or the front legs were cut off first. Without the front legs, struggle is reduced significantly. Bloodloss weakening the cat at the same time. Front legs might be cut off because the cat was defending itself with them.
Killer could then have injuries on his/her arms and legs, that he/she might try to conceal. The front legs could have been kept to deny the cat, even in death, the very weapons that it used to hurt the killer.
This gives the killer the feeling of victory and empowerment as well. Perhaps this is the real trophy item. Why the need for a trophy? To remind them of the glorious battle in which they actually won. Why do they need to prolong this sense of victory? Because in real life, they usually are unable to.
Clean cuts could also mean just a sharp bladed object that anyone can find. Without much of a struggle, a cut can be made easily. If there were pieces of chipped bone fragments at the cut, they could have been chopped off. Sawing leaves torn skin usually.
Thats my brief analysis given the current info we have for now. Its amateurish, I know. But I'm being serious here.
Sorry for such a lengthy first post

I love animals(every single one of them, every type of species) and absolutely detest and despise animal abusers because they are such cowards and weaklings.
some links(a lot of helpful info on pet abuser/criminal psychology):
http://www.pet-abuse.com/pages/abuse_connection.phphttp://www.bharatbhasha.com/psychology.php/22053http://www.crimelibrary.com/criminal_mind/psychology/psychopath/1.htmlhttp://www.crimelibrary.com/criminal_mind/psychology/index.htmlThis person is gonna become more and more dangerous.