Joy Sweeney, whose son Derrik Sweeney was one of the three students detained by police, told CNN she was delighted to receive the news.
Sweeney, Gregory Porter and Luke Gates are students from different universities participating in a semester-long, study-abroad program at American University in Cairo.
They were detained Monday on suspicion of throwing the makeshift incendiary devices during anti-government protests in Cairo's Tahrir Square.
A spokesman for Egypt's general prosecutor accused the three of throwing Molotov cocktails and said they didn't have their passports with them when they were detained.
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