Gen 6:4There 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.
Jud 1:6And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
Jude quotes Enoch word for word. Jude trusted Enoch or else he would not have quoted it word for word. Jude says angels were chained until Judgment Day. Where do you think he got that idea?
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Chapter 6]
1 And it came to pass when the children of men had multiplied that in those days were born unto 2 them beautiful and comely daughters. 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, Zaqiel, 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."
http://www.ccel.org/c/charles/otpseudepig/enoch/ENOCH_1.HTM
As Jude states, the angels were punished, bound in a place of darkness until Judgment Day. He KNEW that because HE KNEW what Enoch 1 says.
