Samtex Wangchuck, 21, did not know the victim, said Martin Butterworth, prosecuting at York Magistrates’ Court.
She was on the phone to her partner when Wangchuck grabbed her between the legs from behind.
The cleaner had decided “it would be a good opportunity to commit an offence” when he spotted her on her own in the city centre at about 3.30am and thought she had been drinking, said Mr Butterworth.
She didn’t realise Wangchuck was following her on his bike through the city centre, past the City Walls and towards the suburbs as she walked home after completing her late-night shift at a hospitality venue.
She had phoned her partner when she started her journey home and was talking to him as she walked.
Wangchuck gradually got closer to her and when she was nearly home, she saw him. By then he was off his bike and about 15 to 20 feet away.
She put her key in her front door and Wangchuck sexually assaulted her. She was still on the phone to her partner.
In a personal statement, she said she now ensures that she always has company on the way home.
“I have lived in York my entire life and never been afraid of walking home alone at night until now,” she said. “I am extremely worried now that he may have done this before.”
Mr Butterworth said Wangchuck told police he had sexually assaulted the woman for his own sexual gratification.
Wangchuck, of Park Crescent, The Groves, pleaded guilty to sexual assault committed in February. He had no previous convictions.
A probation report before the court said that Wangchuck was a “risk to women” and that he didn’t appear to understand the effect of his crime on the victim.
York magistrates jailed him for 12 weeks.
“You targeted a lone vulnerable woman at night, believing her to be in drink. You followed her home,” they told him.
They also made him subject to a lifetime restraining order banning him from contacting the victim in any way or going to her home and banned him from following any woman on her own under a five-year sexual harm prevention order. Wangchuck will be on the sex offenders’ register for seven years.
For him, Colin Byrne said it was a very “odd” incident for which Wangchuck was remorseful. He handed in references from Wangchuck’s family about his remorse and his efforts to reform himself since the offence.
The public would be better protected if Wangchuck could be given a suspended sentence under which he could work with probation officers to tackle the cause of his offending, said Mr Byrne.
He had already had a taste of custody as he had been remanded in custody following his arrest and then released on bail without conditions after pleading guilty.
He worked nights as a cleaner and had finished work early that night.
