Sins of the Angels (the Watchers)

Genesis 6:1
And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them,
2 That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.
3 And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.
4 There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
5 And GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.
6 And it repented the LORD that he had made man on the earth, and it grieved him at his heart.
7 And the LORD said, I will destroy man whom I have created from the face of the earth; both man, and beast, and the creeping thing, and the fowls of the air; for it repenteth me that I have made them.
8 But Noah found grace in the eyes of the LORD.
9 These are the generations of Noah: Noah was a just man and perfect in his generations, and Noah walked with God.
10 And Noah begat three sons, Shem, Ham, and Japheth.
11 The earth also was corrupt before God, and the earth was filled with violence.
12 And God looked upon the earth, and, behold, it was corrupt; for all flesh had corrupted his way upon the earth.
13 And God said unto Noah, The end of all flesh is come before me; for the earth is filled with violence through them; and, behold, I will destroy them with the earth.

The Book of Enoch
Chapter 6
1 And it came to pass when the children of men had multiplied that in those days were born unto them beautiful and comely daughters.
2 And the angels, the children of the heaven, saw and lusted after them, and said to one another: 'Come, let us choose us wives from among the children of men
3 and beget us children.' And Semjaza, who was their leader, said unto them: 'I fear ye will not
4 indeed agree to do this deed, and I alone shall have to pay the penalty of a great sin.' And they all answered him and said: 'Let us all swear an oath, and all bind ourselves by mutual imprecations
5 not to abandon this plan but to do this thing.' Then sware they all together and bound themselves
6 by mutual imprecations upon it. And they were in all two hundred; who descended in the days of Jared on the summit of Mount Hermon, and they called it Mount Hermon, because they had sworn
7 and bound themselves by mutual imprecations upon it. And these are the names of their leaders: Samlazaz, their leader, Araklba, Rameel, Kokablel, Tamlel, Ramlel, Danel, Ezeqeel, Baraqijal,
8 Asael, Armaros, Batarel, Ananel, Zaq1el, Samsapeel, Satarel, Turel, Jomjael, Sariel. These are their chiefs of tens.

Chapter 7
1 And all the others together with them took unto themselves wives, and each chose for himself one, and they began to go in unto them and to defile themselves with them, and they taught them charms
2 and enchantments, and the cutting of roots, and made them acquainted with plants. And they
3 became pregnant, and they bare great giants, whose height was three thousand ells: Who consumed
4 all the acquisitions of men. And when men could no longer sustain them, the giants turned against
5 them and devoured mankind. And they began to sin against birds, and beasts, and reptiles, and
6 fish, and to devour one another's flesh, and drink the blood. Then the earth laid accusation against the lawless ones.

Chapter 8
1 And Azazel taught men to make swords, and knives, and shields, and breastplates, and made known to them the metals of the earth and the art of working them, and bracelets, and ornaments, and the use of antimony, and the beautifying of the eyelids, and all kinds of costly stones, and all
2 colouring tinctures. And there arose much godlessness, and they committed fornication, and they
3 were led astray, and became corrupt in all their ways. Semjaza taught enchantments, and root-cuttings, 'Armaros the resolving of enchantments, Baraqijal (taught) astrology, Kokabel the constellations, Ezeqeel the knowledge of the clouds, Araqiel the signs of the earth, Shamsiel the signs of the sun, and Sariel the course of the moon. And as men perished, they cried, and their cry went up to heaven . .