After arriving at the crime scene get a police uniform from the back of the police van down the alley. Fast talk your way past some guards and enter the warehouse. Investigate the bodies and leave. Call Teng and ask what to do next.
Head to Central Hospital. Get a disguise from the ambulance and go inside. Check the hospital records. Bug Doctor Tsang's office and crack his safe before he comes back. Leave the hospital and return the uniform.
Call Teng to check in on the case. She'll inform you that Calvin is the next target. Quickly get to Calvin, then action hijack the kidnapper's car and drive to Wah Fi Storage. Call Teng to finish the mission.