A man who grabbed a young woman in a dark alley in a bid to sexually assault her has been detained in a psychiatric hospital.

Mark Roberts, of Whitstable, followedhis victim for 20 minutes before running at her from behind and dragging her to the ground in Canterbury.

Roberts, 47, put his hand over the woman’s mouth to stifle her screams, but she managed to make enough noise to alert a neighbour.

Roberts, who has paranoid schizophrenia, was handed a hospital order at Canterbury Crown Court on Thursday.

He will only be released when a mental health tribunal is satisfied he no longer poses a risk to the public.

Judge Simon James told Roberts: “Your victim, who was a complete stranger to you, was understandably petrified.

“She described how you were immediately and without warning ‘on and over her’ and how you clasped your gloved hands around her mouth in an effort to stifle her screams.

“You pushed her and held her down onto the adjacent grass bank, such that she was unable to move or get up.

“Although absolutely terrified and feeling overpowered, she screamed out as loud as she could.

“Mercifully, her desperate screams for help were heard by another young woman whose home was adjacent to the alleyway.”

The court heard the eyewitness saw the attack unfold outside her window last year and yelled loudly at Roberts, causing him to let go.

As he walked back towards the city centre the witness and others nearby rushed to the distressed woman’s aid.

In a police interview, the victim described the terror she felt while trying to fend off her attacker on the quiet track joining Beaconsfield Road and Beverly Meadow, on .

“My whole body was in shock and I couldn’t stop crying - I was absolutely terrified,” she said.

“I have never felt so relieved that someone had heard me - I thought that nobody ever would.

“I thought ‘I’m not going to get out of this.’ ”

The court heard Roberts, of no fixed abode, was arrested the following day.

He was found to be in possession of a rucksack containing women’s underwear, duct tape and a pair of shoe laces tied together with slip knots at both ends.

Before the trial, psychiatrists informed the court that Roberts had “well established delusional beliefs, which amount to a recognised mental illness”.

Roberts argued that he restrained the woman because he suspected she was conspiring to use a secret mind-control device against him.

But medical evidence read out in court stressed his illness does not stop him for being able to tell right from wrong.

Following his trial in December last year, the jury rejected Robert’s explanation, finding instead the attack was sexually motivated.

He was convicted of committing an offence with intent to commit a sexual offence and assault occasioning actual bodily harm.

During the sentencing hearing, Judge James told Roberts: “[The eye-witness’s] intervention clearly disturbed you and I have no doubt that it saved your victim from an even worse fate.

“I am forced to the sure conclusion that had you not been interrupted by a timely intervention you would have gone on to commit a serious sexual assault.”

“My whole body was in shock and I couldn’t stop crying, I was absolutely terrified...”

Roberts’ doctor, Dr Oluwole, recommended on Thursday that he be dealt with by way of a hospital order with a restriction order.

“I have considered the amount of premeditation involved in this serious offence, the amount of violence used and the psychological harm that was caused to the victim,” said Dr Oluwole.

“Mr Roberts does not have a record of previous conviction for sexual offences, but the day after he was seen in a public place essentially masturbating.

“Although his genitals were not exposed, he was talking to a child.

“I’ve also considered the risk of Mr Roberts committing further offences, given his current mental state and that he is at the early stages of treatment for paranoid schizophrenia and has paraphilic interests.”

Judge James told Roberts his actions amounted to “random and completely unjustified sexual violence”.

“You are, it seems to me, unable or unwilling to comprehend reality and therefore remain someone who will seek to both use and justify the use of what is in fact random and completely unjustified sexual violence.

“You have shown no remorse and little if any empathy with your victim.

“Although I remain sceptical as to whether you are an individual who has the capacity to engage with treatment and make meaningful changes, it seems I must accept the expert opinion that such might be achievable.

“You will be detained in hospital for treatment of your mental illness and will only be released when the mental health tribunal is satisfied that you no longer pose an unmanageable risk of causing significant harm to others.”

The judge also said that the woman who helped the victim should be formally recognised for her brave and selfless conduct.

He recommended she should receive a High Sheriff Award.