Matthew's account:
20 When, now, it had become evening, he was reclining at the table with the twelve disciples. 21 While they were eating, he said: “Truly I say to YOU , One of YOU will betray me.” 22 Being very much grieved at this, they commenced each and every one to say to him: “Lord, it is not I, is it?” 23 In reply he said: “He that dips his hand with me in the bowl is the one that will betray me. 24 True, the Son of man is going away, just as it is written concerning him, but woe to that man through whom the Son of man is betrayed! It would have been finer for him if that man had not been born.” 25 By way of reply Judas, who was about to betray him, said: “It is not I, is it, Rabbi?” He said to him: “You yourself said [it].”
26 As they continued eating, Jesus took a loaf and, after saying a blessing, he broke it and, giving it to the disciples, he said: “T AKE , eat. This means my body.” 27 Also, he took a cup and, having given thanks, he gave it to them, saying: “Drink out of it, all of YOU ; 28 for this means my ‘blood of the covenant,’ which is to be poured out in behalf of many for forgiveness of sins. 29 But I tell YOU , I will by no means drink henceforth any of this product of the vine until that day when I drink it new with YOU in the kingdom of my Father.” 30 Finally, after singing praises, they went out to the Mount of Olives.
No mention of Judas... being there, coming or going...
Mark's account:
17 After evening had fallen he came with the twelve. 18 And as they were reclining at the table and eating, Jesus said: “Truly I say to YOU , One of YOU , who is eating with me, will betray me.” 19 They started to be grieved and to say to him one by one: “It is not I, is it?” 20 He said to them: “It is one of the twelve, who is dipping with me into the common bowl. 21 True, the Son of man is going away, just as it is written concerning him, but woe to that man through whom the Son of man is betrayed! It would have been finer for that man if he had not been born.”
22 And as they continued eating, he took a loaf, said a blessing, broke it and gave it to them, and said: “Take it, this means my body.” 23 And taking a cup, he offered thanks and gave it to them, and they all drank out of it. 24 And he said to them: “This means my ‘blood of the covenant,’ which is to be poured out in behalf of many. 25 Truly I say to YOU , I shall by no means drink anymore of the product of the vine until that day when I drink it new in the kingdom of God.” 26 Finally, after singing praises, they went out to the Mount of Olives.
Judas is mentioned as the betrayer...yet shows him as sharing the meal. No mention of him leaving.
Luke's account:
14 At length when the hour came, he reclined at the table, and the apostles with him. 15 And he said to them: “I have greatly desired to eat this passover with YOU before I suffer; 16 for I tell YOU , I will not eat it again until it becomes fulfilled in the kingdom of God.” 17 And, accepting a cup, he gave thanks and said: “Take this and pass it from one to the other among yourselves; 18 for I tell YOU , From now on I will not drink again from the product of the vine until the kingdom of God arrives.”
19 Also, he took a loaf, gave thanks, broke it, and gave it to them, saying: “This means my body which is to be given in YOUR behalf. Keep doing this in remembrance of me.” 20 Also, the cup in the same way after they had the evening meal, he saying: “This cup means the new covenant by virtue of my blood, which is to be poured out in YOUR behalf.
21 “But, look! the hand of my betrayer is with me at the table. 22 Because the Son of man is going his way according to what is marked out; all the same, woe to that man through whom he is betrayed!” 23 So they started to discuss among themselves the question of which of them would really be the one that was about to do this.
24 However, there also arose a heated dispute among them over which one of them seemed to be greatest. 25 But he said to them: “The kings of the nations lord it over them, and those having authority over them are called Benefactors. 26 Y OU , though, are not to be that way. But let him that is the greatest among YOU become as the youngest, and the one acting as chief as the one ministering. 27 For which one is greater, the one reclining at the table or the one ministering? Is it not the one reclining at the table? But I am in YOUR midst as the one ministering.
Here we see that Judas is at the table with the twelve when the meal is taken. No mention of him leaving...
John's account:
21 After saying these things, Jesus became troubled in spirit, and he bore witness and said: “Most truly I say to YOU , One of YOU will betray me.” 22 The disciples began to look at one another, being at a loss as to which one he was saying [it] about. 23 There was reclining in front of Jesus’ bosom one of his disciples, and Jesus loved him. 24 Therefore Simon Peter nodded to this one and said to him: “Tell who it is about whom he is saying [it].” 25 So the latter leaned back upon the breast of Jesus and said to him: “Lord, who is it?” 26 Therefore Jesus answered: “It is that one to whom I shall give the morsel that I dip.” And so, having dipped the morsel, he took and gave it to Judas, the son of Simon Is·car´i·ot. 27 And after the morsel then Satan entered into the latter. Jesus, therefore, said to him: “What you are doing get done more quickly.” 28 However, none of those reclining at the table knew for what purpose he said this to him. 29 Some, in fact, were imagining, since Judas was holding the money box, that Jesus was telling him: “Buy what things we need for the festival,” or that he should give something to the poor. 30 Therefore, after he received the morsel, he went out immediately. And it was night.
Here Judas dips the morsel and then leaves. Only in this account does it mention Judas leaving.
Another interesting thing about the JW teaching of this event. They pass off the Passover and the "new" Lord's Evening Meal as two seperate events that take place the same night in the same room. However the text of the Bible does not support that. They are clearly having a Passover meal and Jesus makes some symbolic comments about the bread and wine as they eat. Judas was there, he joined in and then, according to John, left.