"Oh, don't get me wrong. My DNA is all over that girl, but that doesn't mean I killed her."
The son of a successful businessman, Syd met James Barrett when they were both in middle school. The two became good friends, despite their different socio-economic backgrounds, and wound up committing a number of petty crimes together, such as shoplifting and vandalism. They also once burned a vacant house to the ground. They were once charged with assault but the charges were dropped. True to character, Syd cheated on his SATs but was told on by his then-girlfriend. A woman named Kelly Grabeel also filed a complaint for some sex-related offense against Syd but later dropped all the charges. A divisional lacrosse player, Syd broke his left arm during a game sometime before "J.J." According to Morgan, it happened because he was distracted by a rejection from Chapel Hill (presumably a prestigious school) and had already told all of his friends that he was going to attend it. A few days prior to "J.J.", Syd and James met Kate Joyce, who was already familiar with the latter after meeting him at his workplace, and drove her to her hotel room, taking pictures of themselves along the way. At the room, he had sex with Kate, and James attempted to do the same but she rejected him. Unbeknownst to him, James decided to get revenge on Kate; he drugged and abducted her and brought her to his boat, later going out on the ocean and shoving her overboard in an area where sharks would be feeding at that time of the day as fishermen dumped their catch loads.
When Kate's disappearance goes public, he and James are suspected and interrogated by the BAU and local police. He is let off the hook when his behavior tells the BAU that he is getting off from the attention he is receiving. Eventually, Kate is rescued and James is identified as her abductor and attempted killer, subsequently getting arrested.
Just like how the Kate Joyce case as a whole is similar in several ways to the disappearance of Natalee Holloway, Syd borrows elements from the main suspect in that case, Joran van der Sloot. Both were the more dominant, charismatic, and sexually successful among the group of suspects; came from a wealthy family; enjoyed sports; and seemed to revel in the attention given to them by the media and law enforcement.