You can, but hopefully LE, and more importantly FBI, would be able to spot/see the "noise" in the photo to know it is a picture of a picture (a similar thing happens when you scan an old photo on to your computer from a printer, or the like. it creates "artifacts" in the image and will loose sharpness around the edges and add color noise.)
There is a problem with uploading pictures to Twitter that I am sure LE/FBI finds their ways around, because when you upload to twitter w/o the device the picture was sent from (lets say the picture was taken on the phone, then uploaded to a personal computer, then to twitter) it loses the exif data at the twitter upload. The only device to have the true "stamp" of that image would be on the phone, and likely the computer -- if it was sent to the computer after being taken.
That's the long version. I believe Sierra uploaded from the phone to twitter.
(How I know all this; Pro photog (freelance journalism), and I have studied the twitter uploads/facebook uploads ad nauseam in some cases here.)