Using a profile of the Ripper drawn up by the FBI in 1988 to mark the centenary of his killings, Trow began looking for a local suspect who hailed from Whitechapel’s lower social classes, was the victim of a broken home, and was someone who had worked as either a butcher, a mortuary worker or a medical examiner’s assistant. He also used modern geographical profiling techniques that can pinpoint where a suspect might live depending on the nature and location of their killings.
The odd thing is that so much time has passed that there is difference between having solid evidence and having no evidence at all. Anyone living in the London area in 1888 can become a potential suspect and there's nothing you can do to fully prove or disprove your case. It's historical wankery at it's finest.