I think people came to the conclusion that Gehenna is Hell from the scriptures that contain the word. Here are ALL the New Testament verse that contain the word “Gehenna.” These verses are quoted from the NKJV which translates “Gehenna” as “hell.” I have added the word “Gehenna” in brackets after the word “hell.”
Mt 5:22 “But I say to you that whoever is angry with his brother without a cause shall be in danger of the judgment. And whoever says to his brother, ‘Raca!’ shall be in danger of the council. But whoever says, ‘You fool!’ shall be in danger of hell [Gehenna] fire.
Mt 5:29 “If your right eye causes you to sin, pluck it out and cast it from you; for it is more profitable for you that one of your members perish, than for your whole body to be cast into hell. [Gehenna]
Mt 5:30 “And if your right hand causes you to sin, cut it off and cast it from you; for it is more profitable for you that one of your members perish, than for your whole body to be cast into hell. [Gehenna]
Mt 10:28 “And do not fear those who kill the body but cannot kill the soul. But rather fear Him who is able to destroy both soul and body in hell. [Gehenna]
Mt 18:9 “And if your eye causes you to sin, pluck it out and cast it from you. It is better for you to enter into life with one eye, rather than having two eyes, to be cast into hell [Gehenna] fire.
Mt 23:15 “Woe to you, scribes and Pharisees, hypocrites! For you travel land and sea to win one proselyte, and when he is won, you make him twice as much a son of hell [Gehenna] as yourselves.
Mt 23:33 “Serpents, brood of vipers! How can you escape the condemnation of hell?. [Gehenna]
Mr 9:43 “If your hand causes you to sin, cut it off. It is better for you to enter into life maimed, rather than having two hands, to go to hell, [Gehenna]<1067> into the fire that shall never be quenched —
Mr 9:45 “And if your foot causes you to sin, cut it off. It is better for you to enter life lame, rather than having two feet, to be cast into hell [Gehenna], into the fire that shall never be quenched —
Mr 9:47 “And if your eye causes you to sin, pluck it out. It is better for you to enter the kingdom of God with one eye, rather than having two eyes, to be cast into hell [Gehenna] fire —
Lu 12:5 “But I will show you whom you should fear: Fear Him who, after He has killed, has power to cast into hell [Gehenna] ; yes, I say to you, fear Him!
Jas 3:6 And the tongue is a fire, a world of iniquity. The tongue is so set among our members that it defiles the whole body, and sets on fire the course of nature; and it is set on fire by hell.[Gehenna].