Question about jack the ripper?

I,m interested in this case as so many of us are but i have been reading a book. That was brought for me for xmas with the victims death certificates on cd rom what not. Ive been reading up on this case and the first person killed martha Tabram had her throat cut jaggedly and a bayonet was used for one wound by a left handed person and the rest of the wounds inflicted by a penkinfe and a right handed person. The question i have though is with the other women it was definately a person with surgical knowledge. So does this mean that Martha Tabram was done by someone completely different because the wounds and the throat were not done by a professional. I know theres is loads of curiosity about the ripper but from what ive read so far only 3 women were killed by the same person by the way the wounds are and what not. Anyone got any ideas or do you think all of the murders were the same person trying to cover himself up? good question aye. Would love to know your thoughts.