Evagrius Scholasticus, Ecclesiastical History, IV, XXXII:

Justinian I
Justinianus I
Ιουστινιανός I

"There was also another quality latent in the character of Justinian, a depravity which exceeded any bestiality which can be imagined; and whether this was a defect of his natural character, or whether it was the outgrowth of cowardice and fear, I am unable to say, but in any case it manifested itself as a result of the popular Nika Insurrection. For he seemed to be absolutely devoted to one of the two Factions, the Blues namely, and to such a degree that these actually used to murder their opponents in cold blood in broad daylight and in the middle of the city, and not only did they suffer no penalty, but they actually were counted worthy of prizes of honour. And they were permitted even to enter houses and to gather as plunder the valuables therein and to force the inhabitants to pay for their own lives. And if any of the magistrates tried to stop them, he thereby endangered his own life. Thus, for instance, a certain man administering the government of the East, because he disciplined with stripes some of the unruly element, was himself flogged in the very middle of the city and roughly handled. And Callinicus, the Governor of Cilicia, because he inflicted the punishment of the law upon two Cilician murderers, Pautus and Faustinus, who had assaulted him and made an attempt upon his life, was impaled, thus paying the penalty for his correct judgment and his support of the laws. Consequently the members of the opposite Faction went off into exile, and being received by no one at all, but being driven away from every place like polluted creatures, they proceeded to waylay travellers, both robbing and murdering them, so that every place was full of violent deaths and highway robbery and the other sorts of crime. Occasionally too he went over to the opposite side and began to destroy them, allowing the laws which he had abandoned to run riot through the cities like barbarians. And to tell of all these matters in detail, neither words nor time would suffice; yet these examples are sufficient to furnish evidence for all the rest."

Evagrius Scholasticus (also known as Epiphaneia, Ex-Præfectus)
Ecclesiastical History, IV, XXXII - [Tertulian | WorldCat ]
A younger contemporary of Procopius and of Justinian (c. 536‑594)

Cp. Procopius, The Secret History, tr. by Richard Atwater (1927) [Sacred-Texts]
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