Different contemporary investigators named different suspects.
Inspector Abberline suspected Severin Klosowski (alias George Chapman).
Chief Inspector Littlechild suspected Francis Tumblety (we discovered that he was a suspect as recently as 1993 when a letter written by Littlechild turned up).
Sir Macnaghten (later promoted to Chief Constable) wrote memoirs which named Michael Ostrog, Aaron Kosminski and Montague John Druitt as contemporary suspects. Macnaghten's official suspect was Druitt.
He didn't. Jack the Ripper was never caught.
He killed and ripped woman's bodies. The police received a boasting letter from a man claiming to be the killer. It was signed Jack The Ripper.
The London police never held the opinion that Jack the Ripper was murdered... he just stopped killing for reasons known only to him.
The killer refered to himself by several different names, Jack The Ripper and Saucy Jack are just a couple. He obviously had a flare for the dramatic. Jack The Ripper has become almost legend thanks in part to that 'oh so appropriated' name.
Over the course of the Ripper investigation hundreds of letters were sent to police and press. Many people, including PC's at Scotland Yard, thought that only three letters were genuine (written by the killer). This is, of course, just an educated guess.
Walter Richard Sickert.
Frederick George Abberline - Chief Inspector for the London Metropolitan Police.
Thomas Cutbush was named as the Ripper by the Sun newspaper on the 13th February 1894. The possibility of Thomas Cutbush being Jack the Ripper was thoroughly investigated by the police at the time, and shown to be without foundation.
Jack the ripper was the first serial killer to reach the media. The world has eyes on him. It was a scandal about the condition the police was at that time. There were no false starts in this case. There was nothing to go on but the remains of the victims. Even today it takes quite some time to catch a murderer on the run, but in the case of Jack the Ripper, there were many aspects police today would not come across.
police was not as affective as they are now and there was no way of finding pepoles DNA
Jack the Ripper was never caught because forensics and police detection was not advanced enough to apprehend a criminal such as the Ripper. He was also very lucky.
Scotland Yard never claimed to have captured Jack The Ripper and in fact were ridculed for their inablity to catch him. It resulted in many conspiracy theories, some involving the royal family, the police force and even Inspector Fredrick Abberline.