The police drew portraits of the suspects spotted by residents of the neighborhood, gathered some biological traces on-site, and investigated around 500 people, but failed to catch any suspects then.

Throughout the years, the Xuhui district police bureau kept checking the biological traces with police departments outside Shanghai, in the hope of finding a match, and the police in Shandong happened to discover a match with one ex-convict Qin in the province in February.

After investigation, Qin was apprehended by police officers on March 17. The 49-year-old then gave out clues for the other two suspects, which helped the police arrest them.