A lone gunman walked into a midtown Manhattan office building Monday and opened fire, killing four people, including an NYPD officer, before turning the gun on himself.

Officials said the gunman fatally shot himself after his attack, which set off a chaotic scene that rippled out into the heart of Manhattan during rush hour.

Two teams NYPD detectives headed to Las Vegas Tuesday, to execute search warrants at Shane Tamura's home and at a gun store where he legally purchased a revolver on June 12 using a Nevada concealed carry permit,