There are several factors that can be used for why the murderer was never caught, firstly:
There were no witnesses, whether this was part of the murderers plan, to find someone without people, or to kill them somewhere isolated then dump their body elsewhere is unknown. It could be accounted to luck that there were no witnesses, and the people who did come forward to give evidence gave several different descriptions, which contradicted each other. If there was someone who witnessed the murder, maybe he would have been caught.
The victims were prostitutes; people who usually avoided the police anyway. They were easy victims for several reasons. Firstly, they had a dangerous profession anyway, they risked being beaten up and murdered every night, so maybe with a serial killer out their, they didn’t see their chances as any lower or any higher of being murdered. They also really needed the money, to risk going out every night, they were very poor, so they still went out. They would take clients to a place that was isolated from other people, it made it easier for the murder, as noone would hear them, and there would be no witnesses. Also prostitutes were often drunk and vulnerable anyway, making them easier to silence.
Because the killer did not know his victims, it made it harder to solve. It is the same case today with the Washington Sniper. If you target people you have no connection with, then there is no way to relate you to them. You cannot ask other friends or family about other people they knew in their life who might kill them, or who is suspicious. It gives the police no link, so they don’t have much to follow up on. Other than he was killing prostitutes, and there were hundreds in London.
Also, this was one of the first big cases detectives of a poorer area (Whitechapel) had to deal with, their usual methods included rounding up suspicious looking suspects, and patrolling the poorer areas. This was obviously not going to work in this case. Because the Ripper had to blend in, if he wanted prostitutes to go with him. Also, the Ripper’s gruesome mutilation was not what the police were used to dealing with, it was not a domestic murder case, therefore they had no leads, but the Ripper was striking at random prostitutes, therefore they had no idea where he could be.
There was also a lot of misleading evidence. There were hundreds of letters sent in claiming to be from Jack the Ripper. Only 3 of which are considered to be anywhere near liable. Two of which are from the same person, staring with “Dear Boss” for these two letters, it could have been sent in straight after reading the newspaper, or made up from a journalist trying to promote the story. The other one however, came with half a kidney, that looked likely to be taken from one of the victims. Other false leads like Leather Apron were also off-putting.
The anti-semantic writing on the wall, found near Catherine Eddowes’s body, could have also have been a great help, or a disaster. If it was a clue, it was wiped off the wall, and therefore they could not use it to compare handwriting. Or it could be false, leading to riots. The Jews in the past had been blamed for a lot of murders, as they were widely disliked, but still held a lot of money and power in general. Any mention of the killer being Jewish would have lead to riots, which the police did not want on top of trying to catch the killer.
It can be said they did their best using what evidence they had. There was no forensic evidence, finer prints were not used until 1901, there was no DNA evidence, and photography in this case had only just started, it made the police’s job finding evidence difficult with so little of anything to go on. If they had had DNA evidence, more accurate records of criminals and better security (cameras in the streets) then maybe he would have been caught. But because of limited evidence, of the killer leaving no weapons behind, and clothing and possession were later accounted for, the police had little to go on.
The police were also under a lot of pressure from the press and politicians. With the press thinking up of one story after another, it maybe gave the police too many useless leads that wasted their time. The media was constantly bombarding the police force: their usual methods were slow, and not very effective. However now, they were under pressure to catch someone, they had to speed things up, which would have resulted in several wrong suspects, and evidence. They were expected by the public to catch the ripper, after 5 murders that were not prevented after heightened security from the police, it made the public and media put more pressure on.
The killings stopped, there are several suspected reasons for this. However, if the murders had continued, it is entirely feasible that someone would have eventually caught him, with so few prostitutes on the street, and so many metropolitan police.
Some suspected reasons are:
The police were getting to near to catching him, to risky to carry on.
He died, or was imprisoned for another crime. Many deaths went unreported to the police.
Moved to another part of the UK, with not as good as the metropolitan police force, or just simply moved away. Or moved to another country. After the ripper murders, there were several murders in America, with the same pattern. Because of no international links, noone ever linked the two together.
After committing so many crimes and knowing the end was near, killed himself, this too would have carried no concern with the press.
He had killed enough people. This one is most unlikely. It has been observed with other psychopaths and serial killers, they only stop when they have been caught, or die. It was probably not as much of a lust as a fixation.
They caught the Ripper, but it infact was connected to the royal family or government, and it would have been a huge public scandal, and uproar would ensure, so they never told the press, or anyone else in the police force he was caught.