The rebels say the 48 Iranians captured last August were members of the Revolutionary Guards on their way to join pro-government forces. Iran says they were simple pilgrims on their way to a shia shrine.

We may never know the truth of the matter, but the Iranians were exchanged for 2,000 Syrian civilians being held by the government.

New York Times:

The exchange, brokered by Turkey and Qatar, came days after Mr. Assad warned on Sunday that he would not abandon the fight against armed adversaries pressing on the approaches to the Syrian capital, Damascus, and brushed aside calls for him to quit.

While the Iranian Foreign Ministry in Tehran confirmed the release of its citizens in a statement to the official IRNA news agency, precise details of the prisoners being released in exchange for them remained unclear.

But Prime Minister Recep Tayyip Erdogan, a regional power broker allied to the Western and Arab nations seeking Mr. Assad's departure, said he hoped the exchange on Wednesday would lead to freedom for more prisoners in Syria.

"We wish many other innocent people, and people in need, to be released from Syrian jails without delay," Mr. Erdogan said in a televised news conference in Niamey, Nigeria, where he arrived on an official visit.

"This process needs to be appreciated. We are not in a position to say anything more than, 'May this produce some good'."

The 2,000 prisoners released represents a tiny fraction of the number of prisoners it is thought are being held by the Assad regime. It is not uncommon to find the tortured bodies of those taken in massive sweeps by Syrian forces as they move through towns, villages, and neighborhoods. Sometimes, families are summoned to come to the detention center to claim a loved one's body. In some cases, all males over a certain age are rounded up and held for interrogation. Tens of thousands of families across Syria have had no information about their fate.

One more reason why Assad will fight to the bitter end; the murder of captive civilians is just one more bloody sin for which he will someday have to pay.