Note left by Manhattan office gunman asked for his brain to be studied

We are also learning more about those victims. Among the dead, an NYPD officer, a Blackstone executive, a security guard, a 27year-old woman. Another man who is 41 years old is in critical but stable condition. MSNBC investigative correspondent Mark Santia joins us now from the scene. Mark, we are now hearing the gunman was an employee at a Las Vegas casino. What more have you learned about him and his motive? Yeah, we've learned the 27-year-old gunman was a surveillance department employee at the Horseshoe ...