The answer of the thirteenth riddle - Numbers Party
The first paragraph.
Three times of that lone alphabet
Three "special guests" plus one, from the land of plenty states
All were there, celebrated the social gathering.
###
» There're three, plus one people, came from the country which has a lot of states (USA, probably) And they participated in some kind of party? This also contains the question, or shall I say...a hint?
The second paragraph.
Eight, Ninety-nine, and Four
The numbers and symbols of three identities.
Remember that...
###
» These are the numbers that represented those three person. They're the hints to tell you which case of this riddle references to, if you couldn't get it in the first paragraph.
The third paragraph.
Three meanings, dirtied by one dirtiness
Drugs, games, affairs
The illegal acts, the owners were exposed
And so, one of them did play the stupid act
Made the resentment set off on scene
The five-shaped keeper one had brought down the punishment.
###
» Three meanings of three numbers on three persons, confused huh? Let's just assume one of them, probably the culprit of the case, was planing to kill the forth person, as a revenge?
The fourth paragraph.
The not-three lights were switched on
Displayed the alphabet on the also not-three windows
And the trigger was pulled...
Leaving the message of the three fingers and the belt behind
The trick of positions, hidden inside
In that said windows' cemented-owner.
###
» The trick of created an alibi, while the culprit headed to shot the victim (which assumed to be the fourth person). The victim left the dying massage involving 'three fingers' and 'the belt' on the body.
The fifth paragraph.
However, all this person had done was for nothing.
In the end...
One mistake, lead to another
One small card was scarlet, which a loser sure deserved
The cheater lost, then turned back..
And walked away...
###
» The must be some kind of mistake (or mistakes) in the trick, perhaps from the carelessness, so it was seen through. There's mention of red card, a loser, and the cheater, look familar?
The Conclusion
Three times the alphabet = 3K, so the answer is "K". In the 3K Osaka case, Heiji-kun invited Conan-kun, Kogoro-san, and Ran-chan to the 3K restaurant's opening party, as his parent both caught a cold and couldn't go. The owners of the restaurant were the three famous athletes from America. The heavyweight boxing champion:Ricardo Barreira, the leaguer:Mike Norwood, and the goalkeeper:Ray Curtis. The numbers, 8, 99, and 4 referred to these three. Ray was a number 8 on the team, Mike who pitches 160km (99 mph), and the last, Ricardo who always win in 4 rounds.
The news reporter/the fourth person/the victim Ed McCay exposed the three's scandals, the ones in the third paragraph. So one of them wanted to go for revenge. The culprit, which revealed to be Ray by Conan-kun, shot Ed, and used the trick of position to created a plausible alibi. But Ray made a mistake of not washing off the gunpowder which was left on his shoes. Also, Ed left a dying message pointing to him, as the three fingers referred to how Japaneses eat Sushi, and the belt "bandou" is for the number eight. Ray didn't surrender, so Conan-kun kicked a ball to his face, in which he couldn't even block it because of the drugs he used. Then Conan-kun said his weird English, and Ray turned himself in to the police.
(I'm not good at explaining things, sorry guys ^^" But hope at least you understand.)
If you don't like it, just move on to the next riddle, I don't mind ^^