He was seen on the footage carrying the Karrimor backpack that was found in pieces at the scene of the bombing. Also found was the detonator, a $20 12 volt battery, and screws that were used as shrapnel.
His younger brother Hashem was planning another attack, according to authorities.
Hashem is in custody in Libya. His father, said to be an outspoken supporter of Al Qaeda, has also been charged.
The British-born brothers flew from Manchester to Libya April 17. Exactly a month later, on May 17, Salman returned alone after a stopover in Dusseldorf, Germany, a hotbed of Islamic extremism.
Investigators believe the brothers are part of a much wider terror network. Another terrorist may have been nearby as a backup, ready to detonate the bomb if the 22-year-old lost his nerve.
The leak of the surveillance photos to The New York Times has led to a rift between British and American authorities.
The British say they will no longer share information with their American counterparts. Prime Minister Theresa May is expected to confront President Trump over the leaks when they meet in Brussels, Belgium, Thursday at the NATO summit.
"I will make clear to President Trump that intelligence that is shared between our law enforcement agencies must remain secure," she said at a cabinet meeting Thursday.