West Mercia and Warwickshire Police admitted putting the names of two women online in a document viewed 197 times.
The error related to the case against Jamie Reynolds, jailed at 23 for murdering Georgia Williams in 2013.
Judge Jonathan Gosling said the mistake was "careless in the extreme" but not intentional.
Chief Constable David Shaw said the witnesses were named by "human error" and apologised to the women.
After the hearing at Stafford Crown Court one of the women said they "could have been put in a life-threatening situation".
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Judge Gosling said the two witnesses had "suffered seriously" but it was not deliberate contempt of court.
The two forces had put online an independent review by Devon & Cornwall Police which was viewable for 11 days, the court heard.
Judge Gosling said: "The court cannot lawfully impose punishment for the breach unless those responsible are shown to have breached the order with the intention of interfering with the administration of justice."
Georgia Williams' mother Lynnette said: "I can't believe they aren't going to be punished just because they didn't do it on purpose.
"It's complete incompetence again."
One of the victims who cannot be named, said: "I feel let down again for the second time.
"I could have been in a life-threatening situation and we could have been exposed by their incompetence in printing our names."
During his trial, the court heard Reynolds harboured a fascination for strangulation from at least the age of 15.
A psychiatric assessment found he "had the potential to progress to become a serial killer".
During his sentencing, the court heard Reynolds tricked Georgia into going to his house for a photoshoot involving a simulated hanging. He later admitted killing her.
Reynolds, who was 22 at the time of the murder, became one of the youngest in British criminal history to be sentenced to a whole life term in prison.
Two police forces which published witness names online in the case of one of Britain's youngest whole life term killers, will not be prosecuted.