The victims were typically prostitutes who had their throats cut and bodies mutilated. In some cases the bodies were discovered just minutes after the ripper had left the scene. An important detail here is that Jack killed prostitutes, WOMEN prostitutes and NOT MEN.
Discovery Channel made a show named Jack the Ripper: Killer Revealed. In that show, they claimed that a person named Robert Mann is the infamous killer. So, this Robert, has a history of mental problems and he ran away from his mental institution. After he went missing, that's when the killing mania began.
In modern times there has even been some theory that Prince Albert Victor was the murderer. Even with modern police methods, no further light has been shed on the murders in recent times.
Our Theory:
Maybe Jack kills prostitutes because he had a girlfriend who was a prostitute.
About cutting their throats, maybe his girlfriend was a liar and he couldn't take it.
So, cutting their throats out made him a little fine? We're not sure about this.
Other than that, we have no idea what's his problem with prostitutes.
Image sources:
sarcasticgamer.com
pulsorock.com
www.ourstrangeworld.net
www.fromthebalcony.com