Rights group says indiscriminate attacks by Israel caused high civilian death toll.
Abu Taha, a Palestinian from the northern West Bank city of Nablus with Syrian citizenship, was declared dead by a Lebanese army spokesman on September 3 after heavy fighting as the 15-week siege came to an end.
The military said that the other three fighters detained on Saturday were a Saudi, a Syrian and a Tunisian.
The government has said that 222 militants were killed in the fighting and more than 200 arrested, while 167 Lebanese soldiers died.
Court officials have said that the wife of Shaker al-Absi, the Fatah al-Islam leader, retracted on Saturday her earlier testimony that a body she had viewed in a hospital after the siege was that of her husband.
During questioning with Ghassan Oweidat, an investigating magistrate, she said that her identification might have been mistaken.
DNA test results on the body claimed to be that of al-Absi had already revealed that it belonged to a man in his 30s, while al-Absi is 53.
Authorities have said that they believe he fled the camp hours before the army took control and is still at large.