A police officer has been jailed for nine years after he sexually touched a vulnerable six-year-old girl while responding to a disturbance.

Dean Dempster, 35, an officer for Greater Manchester Police (GMP), assaulted the child while on duty in Oldham on December 29 last year, the Crown Prosecution Service (CPS) said.

He was also later found to have downloaded hundreds of indecent images of children over a period of two years, and had superimposed his face on to some of the images.

Dempster was arrested at work the day after the assault following a formal complaint against him, but deleted some material and applications from his personal mobile phone before it was seized, the CPS said.

Another iPhone, four pairs of folded children’s underwear, shredded underwear in a bag, a disc of images, and two hard drives were all recovered during a search of his home.

His phone and iPad contained 104 category A indecent images of children, the most serious, 440 category B images and 2,472 category C images, including almost 200 pseudo images.

A large number of the pseudo images had been superimposed to depict Dempster with children, while examination of his devices suggested he had been downloading the images from December 15 2021 to December 29 last year, the CPS said.

Analysis of his internet usage revealed Dempster had been searching for content of children’s feet.

Dempster was sacked by GMP following an accelerated misconduct hearing, which he did not attend, in May.

In his decision at the hearing, Chief Constable Stephen Watson said the case was “amongst the most distressing of circumstances ever presented to me” and was a “despicable betrayal”.

He said: “(Dempster’s) actions were entirely deliberate and unforced. As a police officer, he knew that his actions were patently unlawful, dreadfully injurious to the wellbeing of a very young victim in the case of the sexual assault; and he should also have recognised that his behaviour was morally reprehensible.”

Dempster, of West Didsbury, Manchester, was sentenced to nine years’ imprisonment at Liverpool Crown Court on Wednesday, the CPS said.

He previously pleaded guilty to sexual assault on a child under 13, six counts of making indecent images of children and two counts of misconduct in public office.

GMP Deputy Chief Constable Terry Woods described Dempster as a “depraved exception” who the force had “wasted no time in dismissing and disowning”.

He said: “Dempster represents the very worst of society. He is not a police officer; he is a child sex offender, a criminal, and he has no right to be near police uniform or serve the public.

“Dempster was rightfully arrested and charged before he could ever work in our communities again.

“We have thoroughly reviewed Dempster’s vetting and can confidently say there was nothing to remotely suggest he had a sexual interest in children.

“He was a man with a career in public service and his record showed no signs of warning.”

Malcolm McHaffie, head of the CPS’s Special Crime Division, said: “Dean Dempster’s actions were abhorrent, and he betrayed the trust placed in him as a serving police officer.

“The sexual assault took place while he was on duty, and there is no doubt that the victim has been deeply affected by being targeted by someone in authority.

“Subsequent searches of Dempster’s devices and his home address revealed further deplorable offending, and he is now facing the consequences of his actions.”