Alexander Dale, 31, grabbed the 11-year-old and pushed her to the floor while she was walking her dog in Cyncoed.
Two days earlier, on October 23, 2024, Dale approached a 15-year-old girl on a bus travelling from Barry and showed her explicit messages on his phone.
Detectives sourced CCTV from the bus and, using Retrospective Facial Recognition, Dale was quickly identified as the suspect.
He was arrested, charged and remanded within a week.
Retrospective Facial Recognition Technology compares still images of faces of unknown subjects against a reference image database.
Further enquires confirmed Dale had used a mobile phone app, linked to his e-mail address, to buy his bus ticket.
He pleaded guilty to sexual assault and inciting a child to engage in sexual activity.
This week, he was sentenced at Newport Crown Court to 23 months in prison and is also subject to a 10-year Sexual Harm Prevention Order (SHPO).
Officer in the case, Detective Constable Emma Partridge said:“Both victims have been incredibly brave to share what happened to them and support the investigation.
“Dale’s actions continue to have a huge impact on their day to day lives including feeling vulnerable on public transport and walking alone.
“I hope today’s sentencing brings the girls some comfort and allows them to regain their confidence to move forward.
“Everyone has the right to feel safe, wherever they are, and South Wales Police does everything possible to keep communities safe and ensure people feel safe when going about their everyday business.
“Stranger incidents like that are very unusual, but when they do happen, we use all available technology and traditional policing methods to bring offenders to justice.”
