After a literal shitload of research into the murder of King Joffrey I have found out who the killer is.
I have narrowed down the possible suspects to a list of six.
Suspect Number One: Winnie The Pooh
Why he hated Joffrey: It was recently revealed that Winnie the Pooh was in fact Darth Vader and that his friend and partner in crime Christopher Robbin was Jack the Ripper. There was a scandal and Pooh's reputation was damaged as a result...And who accused Pooh in the first place of being the famous Victorian serial killer? Joffrey himself! Pooh also wanted to seize power for himself.
Pooh has always hated Joffrey, being a secret admirer of the late Ned Stark and Sean Penn. He knew himself that Neddie was going to die, he just didn't expect him to go out like that.
Evidence: He wasn't seen at Joffrey's wedding...Or was he? If you search for Winnie you can see him in the background somewhere, hiding in the shadows or using his force powers or something.
Suspect Number Two: Hodor
Why he hated Joffrey: Hodor is the puppet master of Westoros who has been trying to seize power since the very beginning. Joffrey was an obvious threat, being a nasty king and all.
Evidence: Hodor? Hodor. Hodor! HOOOOOOOODDDDOOORRRRR!
Suspect Number Three: couldbecousin
Why she hated Joffrey: CBC and Joffrey have always hated each other, Joffrey had nothing against her personally but rather something against her species. The species of weebles. Joffrey ordered the execution of thousands of weebles and with the Starks defeated he could have wiped out the entire species. CBC could have killed Joffrey to save her people...But is she really capable of murder?
Evidence: She wasn't present at the royal wedding (for the obvious reason that all webbles caught in King's Landing are to be arrested on sight) but she is a master of disguise and has multiple contacts inside King's Landing. She could have ordered any of them to kill Joffrey for her before paying to keep them silent (in either blood of gold)
Suspect Number Four: This man
Why he hated Joffrey: I have no fucking idea as to who this man is. I don't know his name, his mother's maiden name, the name of his first pet or any other valid details I need to access his bank account. All I actually have against him is evidence.
Evidence:
Look at that face for one thing... Its extremely suspicious! And the way he appears in the murder mystery thing...It looks like he's toasting the dead King and its suspected that it was poisoned wine that killed Joffrey! This man could be dropping a few hints, playing mind-games with and mindfucking us! 
Suspect Number Five: Some_Bloke
Why he hated Joffrey: Some_Bloke hated Joffrey from the beginning. He was allied with both the Starks and the Targaryens and just about everyone else who was an enemy of Joffrey.
Evidence:: It was rumored that he planned on building a time machine and stopping Joffrey from being born, also he's leading an investigation into the murder which he could easily use to clear his name. He was present at the royal wedding, too and left shortly after Joffrey started to choke.
Final Suspect: Kermit The Frog
Why he hated Joffrey: Siblings, the two had a vicious sibling rivalry and childhood together. On multiple occasions Joffrey tried to have Kermit killed but was unsuccessful. Kermit only recently learned of all attempts. On each occasion Tyrion or Jamie intervened, saving Kermit from death. He is also very sympathetic to webbles.
Evidence: Present at the royal wedding and following the death of Joffrey he is now the true heir to the Iron Throne. He has been seen on multiple occasions with Some_Bloke (including when he left the wedding) leading some to speculate that the two collaborated to kill Joffrey:
I interviewed each suspect, even "This Man" who was nearly impossible to track down. It turns out that his real name is Barry. Barry is innocent of murdering Joffrey and conspiring to murder him. However he is guilty of other crimes...Well he has to be right, I mean how can anyone be innocent with that motherfucking face:
That face just has "I took Madeline Mcann hardy har har" written all over it. It turns out that he conspired to have Princess Diana murdered but I decided not to prosecute him as it would give the news another opportunity to talk about the royal family and completely ignore important things going on in the real world. So Barry has been released and is going to continue his successful career in insurance sales and veterinary care. Good luck to you Barry.
As for the other suspects...Hodor, despite being the legendary puppet master and the chosen one of Westeros...Hodor is completely innocent.
It turns out that Hodor knew that someone else would kill Joffrey and all he needed to do was play the waiting game. Now with Kermit ruling over the seven Kingdoms, Hodor sees this as an achievement.
Which brings me to my next point. All of the other suspects (Winnie the Pooh, couldbecousin, Kermit the Frog and Some_Bloke) all played a crucial part in planning the murder. Of course, with Kermit being the King of Westeros all charges have been dropped and all of the suspects can go home and live the rest of their lives.
Joffrey is dead...Long live King Kermit!
ponds from now on.