A former security chief detained in the investigation into former Prime Minister Rafik Hariri's assassination returned to prison Friday after two days in hospital for heart problems, a Lebanese security official said. Maj. Gen. Raymond Azar, the former chief of Lebanon's military intelligence who was rushed to hospital Wednesday, underwent a heart catheterization Thursday and was released Friday morning. He was taken back to the Roumieh prison in the suburbs of Beirut, where he has been confined since his arrest in August, said the official, who spoke on condition of anonymity because he is not authorized to speak to journalists.Azar is one of four Lebanese generals who were arrested on charges of being involved in the Feb. 14 assassination of Hariri. All the generals were pro-Syrian and had occupied senior positions in Lebanon's security agencies until being forced to step down in the outcry that followed Hariri's murder. They were detained on the recommendation of the U.N. commission investigating the assassination, which issued an interim report in October that implicated the Syrian and Lebanese intelligence services. The Lebanese government praised the report, but Syria rejected it.