Titus Livius (Livy), The History of Rome, Book 40
Evan T. Sage, Ph.D. and Alfred C. Schlesinger, Ph.D., Ed.

24. Demetrius was again accused by Perseus before his father. The intended flight through Paeonia was one charge, and the bribery of certain [p. 77]persons to be his companions on the journey; the¹ forged letter of Titus Quinctius weighed especially heavily against him. [2] Nevertheless no severe sentence was openly pronounced upon him, in order that he might rather be killed through guile, and this not out of any consideration for him personally, but in order that his punishment might not expose the plans against the Romans. [3] When Philip himself had a journey to make from Thessalonica to Demetrias, he sent Demetrius, accompanied by the same Didas, to Astraeum in Paeonia and Perseus to Amphipolis to receive the Thracian hostages. [4] Instructions regarding the murder of his son are said to have been given by him to Didas as they separated. [5] Didas either held or pretended to hold a sacrifice, and being invited to its celebration Demetrius came from Astraeum to Heraclea, and it was during this dinner that it is said that the poison was administered.² [6] Having drained the cup he immediately perceived it, and presently, when his sufferings began and he had retired to his bedroom from the dining-room, complaining of the cruelty of his father and inveighing against the murderous designs of his brother and the crime of Didas, he was being tortured by his agony. [7] Then a certain Thyrsis from Stuberra and Alexander from Beroea were admitted, and putting coverlets over his head and mouth they smothered him. [8] Thus the innocent youth perished, his enemies being not even contented with a single kind of death for him.