1 Enoch 19:1
1 And Uriel said to me: 'Here shall stand the angels who have united with women, and their spirits, taking many different forms, are corrupting mankind and leading them astray to worship demons as gods. Here they shall remain until the day of the great judgment when they will be judged and brought to an end. 2 And the women of the angels who went astray will become sirens.'
Justin Martyr Second Apology 5
But if this idea take possession of some one, that if we acknowledge God as our helper, we should not, as we say, be oppressed and persecuted by the wicked; this, too, I will solve. God, when He had made the whole world, and subjected things earthly to man, and arranged the heavenly elements for the increase of fruits and rotation of the seasons, and appointed this divine law — for these things also He evidently made for man — committed the care of men and of all things under heaven to angels whom He appointed over them. But the angels transgressed this appointment, and were captivated by love of women, and begot children who are those that are called demons; and besides, they afterwards subdued the human race to themselves, partly by magical writings, and partly by fears and the punishments they occasioned, and partly by teaching them to offer sacrifices, and incense, and libations, of which things they stood in need after they were enslaved by lustful passions; and among men they sowed murders, wars, adulteries, intemperate deeds, and all wickedness.
Notes and References
"... In his first apology (ca. 155) Justin defends the Christians against, among other slanders, the charge of atheism. He accuses their detractors of not examining what they say and responding with passion under the guidance of evil demons ... Here Justin argues emphatically that Greek religion is demon-based - a theme which will emerge among other apologists for the faith. But who are these demons who through terror induced humans to call them gods? Justin answers this query in his second apology (circa 161). In it he explains that God entrusted the care of humanity and all things under heaven to angels ... Justin reproduces several aspects of the angel story - their lust, fatherhood, and teachings - but also their role in religion. However, in his version the demons are the offspring of the angels, not apparently the emanations from the giants dead bodies. Here, as in 1 Peter 3:19-20, the basis for Justin's claims is 1 Enoch 19:1. Justin's point is that the gods of Greek mythology, who committed a host of immoral deeds, were actually the evil demons depicted in the Enochic angel tale ..."
VanderKam, James C. The Jewish Apocalyptic Heritage in Early Christianity (pp. 64-65) Fortress Press, 1993