The suspects, the only ones detained until now, were alleged at the time to have had links to Al-Qaeda.
"The security investigations have proven that they were not involved in the attacks," the source said.
The three Belgian, one French and three Egyptian suspects were detained in May 2009 and charged with helping to plan the bombing in a crowded square near the 14th-century Khan El-Khalili market, where tourists shop for Pharaonic and Islamic souvenirs and smoke water pipes at outdoor cafes.
The attack killed a 17-year old French teenager and wounded 20 other people of various nationalities.
A Ministry of Interior statement at the time said the detainees had explosives and ammunition when taken into custody and had been recruited to carry out attacks in Egypt and abroad.
The bombing was the first fatal attack on tourists in Egypt since bombs killed at least 23 people at an Egyptian resort in the Sinai Peninsula in 2006.
