“Jesus’ death as a consequence of crucifixion is indisputable.” Gert Lüdemann
“That he was crucified is as sure as anything historical can ever be.” J.D. Crossan
“The passion of Jesus is part of history.” Geza Vermes
Jesus’ death by crucifixion is “historically certain” Pinchas Lapide
“The single most solid fact about Jesus’ life is his death: he was executed by the Roman prefect Pilate, on or around Passover, in the manner Rome reserved particularly for political insurrectionists, namely, crucifixion.” Paula Fredriksen
“The support for the mode of his death, its agents, and perhaps its co-agents, is overwhelming: Jesus faced a trial before his death, was condemned, and was executed by crucifixion” L.T. Johnson
“One of the most certain facts of history is that Jesus was crucified on orders of the Roman prefect of Judea, Ponitus Pilate.” Bart Ehrman
Muslims, however, believe exactly the opposite. The Qur'an says:
"That they said (in boast), 'We killed Christ Jesus the son of Mary, the Messenger of Allah'; but they killed him not, nor crucified him, but so it was made to appear to them, and those who differ therein are full of doubts, with no (certain) knowledge, but only conjecture to follow, for of a surety they killed him not." 4:157
So history tells us one thing, and the Qur'an tells us something entirely different. (It's apt to note the irony here: the Qur'an calls those who are using evidence 'full of doubts' and following 'conjecture'!)
Now, all Muslims will argue that the Qur'an is correct. In light of the evidence, this requires one of two defenses. They must either say: 1-There is not enough evidence in history to conclude that Jesus died on the cross; or 2-History is wrong and the Qur'an is right.
We have seen that response number 1 is wrong; the proof for Jesus' death by crucifixion is overwhelming! But if a Muslim uses response number 2, he is admitting that the Qur'an goes against the facts. That doesn't automatically mean the Qur'an is wrong, it just puts a heavy burden of proof upon the Qur'an to show itself as reliable by some other means.
So, here's your litmus test to see if you're dialoguing with an honest Muslim investigator.
1 - Provide the evidence for Jesus' death, including the scholarly consensus.
2 - Show your Muslim friend that the Qur'an goes against all the evidence.
3 - See how the Muslim resolves this predicament.
If your Muslim friend says "Well no matter what you say, there's just not enough evidence here" then be assured that the person with whom you are dialoguing is not open to an honest investigation (at least not vocally). If the Muslims responds with "You're right, all of history is against the Qur'an, but the Qur'an is more trustworthy than all of history", you have good reason to believe that you're dealing with an honest investigator.