The exact circumstances of Mr. Shadid’s death and his precise location inside Syria when it happened were not immediately clear.

But Mr. Hicks said that Mr. Shadid, who had asthma and had carried medication with him, began to show symptoms early Thursday, and the symptoms escalated into what became a fatal attack. Mr. Hicks telephoned his editors at The Times, and a few hours later he was able to take Mr. Shadid’s body into Turkey.