U.S. officials told CBS News national security correspondent David Martin the email received by Carl and Marsha Mueller contained three photos of their daughter's body.
One of the pictures depicted the 26-year-old in a white burial shroud, which ISIS claimed proved that they treated her body with dignity. Two photos show slight bruising on her face, the officials said.
Martin reported Tuesday that the U.S. intelligence community verified the photos and confirmed Mueller died "recently." The exact time and manner of her death could not be determined.
ISIS claimed Friday that Mueller was killed when a Jordanian airstrike damaged a building in the extremists' stronghold of Raqqa, Syria. U.S. and Jordanian officials denied that assertion, which the kidnappers repeated in the message sent to the Muellers.
A U.S. intelligence assessment also indicates that Mueller may have been offered as a bride to an ISIS fighter during her captivity, CBS News has learned.
Mueller is the fourth American hostage to be killed by ISIS. She was kidnapped in August 2013 after leaving a hospital in the Syrian city of Aleppo. Mueller had been working with humanitarian groups aiding refugees from Syria's civil war.
ISIS has beheaded three other American hostages -- journalists James Foley and Steven Sotloff, and aid worker Peter Kassig -- along with several other Western hostages. Most recently, it released a video purporting to show a Jordanian air force pilot being burned alive, a killing that sparked outrage across the Muslim world.