As Revelation 11:1-2 mentions that once the abomination of desolation occurs, these two witnesses of God will appear wearing sackcloth and mourning, because their own nation is persecuted by the Antichrist.
Matthew 24:15-17 When ye, therefore, shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand:) Then let them which be in Judaea flee into the mountains: Let him which is on the housetop not come down to take any thing out of his house:
Revelation 11:4 These are the two olive trees, and the two candlesticks standing before the God of the earth.
In regards to these two witnesses, they are referred to as the olive trees and candlesticks.
Revelation 11:5 And if any man will hurt them, fire proceedeth out of their mouth, and devoureth their enemies: and if any man will hurt them, he must in this manner be killed.
These two witnesses will have the power to destroy the Antichrist. The days of God’s grace and love are over because this time, God will send his representatives to judge and take control of the chaos; justice will be served.
By analyzing these few verses and attempting to make sense of them, we can indicate that one of the witnesses will be Elijah because he had the power to shut heaven so that it did not rain.
Revelation 11:6 These have power to shut heaven, that it rain not in the days of their prophecy: and have power over waters to turn them to blood, and to smite the earth with all plagues, as often as they will.
As we know from the Book of Exodus, Moses was able to turn water into blood as appointed by God and smite the Egyptians with plagues. So the other witness would have to be Moses.
Malachi 4:4-6 Remember ye the law of Moses my servant, which I commanded unto him in Horeb for all Israel, with the statutes and judgments. Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the Lord : And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse.
Before God actually comes down at the end of the tribulation, He would send down Elijah first and told the Israelites to remember the law of Moses.
Moses and Elijah share one similarity, which is that people were trying to search for their dead bodies but could not find any trace at all. This was clearly mentioned in Deuteronomy 34:5-6.
Deuteronomy 34:5-6 So Moses the servant of the Lord died there in the land of Moab, according to the word of the Lord. And he buried him in a valley in the land of Moab, over against Bethpeor: but no man knoweth of his sepulchre unto this day.
Also, see Exodus 33:20-22 cf 1 King 17:1 that Moses and Elijah will be God‘s chosen witnesses to be sent to earth in the latter 3.5 years of tribulation to assist the suffering Israelites.