A possible suspect could be a family member. There could be some sort of family feud or inheritance issue. For example, if there was a large sum of money or a powerful heirloom involved, a greedy family member might have seen Amy as an obstacle and decided to have her shot to get what they wanted.
It could be an ex - lover. Maybe they had a bitter break - up and the ex - lover was filled with jealousy or revenge. Another suspect could be a business rival if Amy was involved in some sort of cut - throat business environment.
In a mystery - type of fanfic, it might be a stranger who was part of a larger conspiracy. Maybe there was a secret organization that targeted Amy because she knew something she shouldn't. Or it could be a person who was misinformed about Amy and thought she was a threat to something they held dear.
One possibility is that it could be about the events leading up to Amy getting shot. Maybe there was some sort of mystery or conflict in her life, like she was involved in a dangerous situation or had made some enemies. Then the fanfic would detail the actual moment of her getting shot, the shock and pain she experiences.
A jealous rival at the ranch could be a likely suspect. Maybe someone who is envious of Amy's skills with horses or her popularity at the ranch. Another suspect could be a disgruntled former employee who was fired by Amy's family and holds a grudge. It could also be someone from a competing ranch who wants to disrupt the Fleming ranch's operations by harming Amy.
It could be an ex - boyfriend who was jealous and wanted revenge. Maybe he couldn't handle the break - up and decided to harm her in this extreme way.
A possible suspect could be an informant who has turned on Tony. Maybe the informant was promised a better deal by another party if they got rid of Tony. Also, it could be a new criminal on the scene who sees Tony as a threat. This new criminal might be trying to establish their power and reputation, and taking out a well - known NCIS agent like Tony would be a big statement. Another suspect could be a person with a grudge against the NCIS in general, and Tony just happens to be an easy target.
Perhaps it's an insider within the law enforcement or criminal justice system who has a vendetta against the BAU. Maybe they disagreed with the way Derek and his team operate and decided to take matters into their own hands. It could be someone who feels that the BAU has too much power and is trying to send a message.
Perhaps a mysterious stranger who has some unknown vendetta against the Heartland family. This person could have been lurking around the ranch for a while, waiting for the perfect opportunity to strike. Or it could be someone within the community who has a hidden agenda and sees Amy as an obstacle to their plans.
Well, it could be a rival of Ciel's in business or in a social setting. Maybe someone who is jealous of his status or wealth and sees shooting him as a way to get ahead.
A rival law enforcement agency member could be a suspect. Maybe they see Deeks as a threat to their own investigations or operations and decide to take him out. It could be a power play within the world of law enforcement.
It could be an old enemy from Beckett's past. Maybe someone they put in jail a long time ago, who has now been released and is seeking revenge.
It could be a random act of violence by a criminal who was in the wrong place at the wrong time. There are some bad elements in the area where Blaine was and they just targeted him without any specific reason other than opportunity.