Wenwa Chao, 53, was shot and killed on January 19, 2010, in the 200 block of North Chandler Avenue in Monterey Park, California. Chao and his girlfriend, 40-year-old Jenny Sor, were visiting a senior housing facility where Chao’s father lived when a man followed Sor into the building through a glass patio door and opened fire just before 8 p.m. Both victims were pronounced dead at the scene.

Authorities say the alleged shooter was Richard Vithya Tauch, 45 at the time, identified as Sor’s ex-boyfriend; jealousy was reported as the likely motive. Tauch was arrested the next day and booked on suspicion of double murder. The killing involved premeditated actions including hiding in Sor’s car at her workplace and following her to the facility.

What information might help flesh out the timeline that night or explain how the shooter gained access to the building?