Titus Livius (Livy), The History of Rome, Book 40
William A. McDevitte, Sen. Class. Mod. Ex. Schol. A.B.T.C.D., Ed.

24. Perseus now brought before his father a second formal accusation against Demetrius. His preparations for flight through Paeonia were alleged against him, and his having bribed certain persons to accompany him on the journey; but the forged letter of Titus Quintius pressed hardest on him. [2] There was, however, no severe sentence pronounced openly, in order that he might be put to death in secrecy, which they considered a preferable course: nor was this done through regard for himself, but lest the inflicting punishment on him might unmask designs against the Romans. [3] The king himself having occasion to go from Thessalonica to Demetrias, sent Demetrius, with the same attendant Didas, to Astraeum in Paeonia, and Perseus to Amphipolis, to receive hostages from the Thracians, and [4??] is said, on parting with Didas, to have given him directions to put his son to death. A sacrifice was either intended or counterfeited by Didas, and Demetrius, being invited to be present at the solemnity, came from Astraeum to Heraclea. [5] It is said that poison was administered to him in that supper. [6] The moment he had swallowed the draught, he was conscious of its deadly properties; and being quickly after seized with violent pains, left the banquet, [p. 1881]and retired to a chamber, where he continued for some time in agony, complaining of the cruelty of his father, inveighing against the fratricide of Perseus, and the villany of Didas. [7] Then one Thyrsis of Stubera, and one Alexander of Berœa, were sent in, who, covering his head and mouth with blankets, suffocated him. [8] In this manner perished that innocent youth, since in his case his enemies were not even content with a common kind of murder.