Drowning
He dived into the water after watching Morgan dive in to save their UnSub's latest victim. He'd been kidnapping and torturing women that looked like his ex-wife. He'd abused her and trapped her causing her to end up jumping into this lake and committing suicide.
He'd now discovered someone who was almost the spitting image. He'd just driven his car into the lake. Morgan had dived in to save the latest victim so he dived in after to make sure there were no complications.
Morgan succeeded in getting her away from their UnSub just when he realised what was happening and pulled her back. Hotch appeared the other side and pulled the trigger on his glock.
The UnSub fell back dead and Morgan swam to the surface with her not looking back. He rose to the surface and dragged her onto the bank.
He saw she wasn't breathing so he started performing CPR.
Rossi looked around and his chest tightened. Where was Aaron? Surely he should have arisen to the surface by now. Something had to have gone wrong.
Without a second thought he dived into the water. He had to save him. He had to know how he felt. He couldn't live without him; his heart wouldn't bear it. Often he'd wondered what it would be like to be with him.
Aaron could feel something wrap around his lower leg and tugged as hard as he could but it only got tighter. He kept pulling but it just kept getting tighter.
As the water filled his lungs and stung his eyes he thought he could not go this way. He couldn't leave his son an orphan. He couldn't leave without letting Dave know how much he meant to him. He'd often wondered what it would be like to kiss him.
Damn this really stung and he found it hard to keep his eyes open. He started to close his eyes when he felt something by his leg.
He found a vine wrapping its way around Aaron's leg and ripped it as hard as he could off his leg. Thankfully he managed to succeed and swam with him to the top of the surface.
He dragged him onto the bank and immediately commenced CPR. He kept performing CPR with tears in his eyes.
"Come on, Aaron," he cried. "Come on, open your eyes. I love you." He pressed his lips onto his again and breathed into his lungs.