FAA registry search shows it is owned by a Fractional corporation in Las Vegas probably leased to fly charter flights. Having done much of the same type of Lear Jet flying with departures after their concert in the wee hours I understand if they find out fatigue had something to do with the crash.
Sinatra's mothers Lear out of Palm Springs was before his Las Vegas show when they turned west into the mountains so must have been in the early evening. My buddy flew Frank in our charter Lear 25 for a long time after that crash. He still has two bottles of Blue Eyes wine Frank gave him for Christmas one year. The FO drank his two bottles, don't know if they are worth anything after all these years.