Detectives trained to memorise faces are trawling CCTV footage.
Lucy's body was found near Southampton Sports Centre on July 26.
Officers have scoured more than 4,000 hours of CCTV footage.
Chinese authorities have arrested a man after the country’s advanced facial recognition technology spotted him within a huge concert crowd.
China has a network of over 170 million cameras.
The victims include a same-sex couple, who say they were targeted for being gay.
The 18-year-old is on trial for attempted murder.