A man allegedly touched a woman inappropriately while she walked along a main road in St Albans.
Raj Patel, 43, of Ladies Grove, St Albans, has been charged with sexual assault and remanded to custody.
Patel is thought to have approached a woman on Victoria Street on Saturday March 12 at around 9pm.
He allegedly launched a sexual assault on a woman as she approached the junction with Marlborough Road, between St Albans City station and the city centre.
Hertfordshire Constabulary officers said the victim described a "frightening" ordeal and that a bystander rushed to the victim's aid.
They are investigating this incident, along with a second incident from the same evening at around 8.55pm, also on Victoria Street.
Detective Adam Haines said he would like to hear from anybody who may have information about the incident.
Detective Haines said: "This was understandably a frightening ordeal for the victim.
"But I would like to reassure the public that we have arrested and charged a man in connection with the report.
"A thorough investigation is underway and we are keen to trace any witnesses or anyone with information to get in touch.
"We’re particularly keen to hear from the good Samaritan who assisted the victim.
"Are you this man? Please get in touch if so.
"We also believe there may have been a second incident that may be linked where a group of three women were also confronted by a man in Victoria Street/Chequer Street at around 8.55pm.
"They may have important information that could assist us as well as another member of the public who chased a man down Victoria Street.
"If this was you, please get in contact as you may be able to help with our enquiries."
Detective Haines said that dashcam footage from cars on the thoroughfare should be checked.
He said that he can receive emails to Adam.Haines@herts.police.uk or by phone on 101.
Witnesses should quote crime reference 41/20285/22.
Reports can also be made online (https://www.herts.police.uk/ ) , or anonymously to Crimestoppers on 0800 555 111.
Patel is due to appear at Stevenage Magistrates' Court on April 29.
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