Many Saints throughout history were martyred because they would not deny their faith in Jesus Christ.
9 And when he had opened the fifth seal, I saw under the altar the souls of them that were slain for the word of God, and for the testimony which they held:
10 And they cried with a loud voice, saying, How long, O Lord, holy and true, dost thou not judge and avenge our blood on them that dwell on the earth?
11 And white robes were given unto every one of them; and it was said unto them, that they should rest yet for a little season, until their fellowservants also and their brethren, that should be killed as they were, should be fulfilled.
Edward Stevenson wrote:
“During the [Prophet Joseph Smith’s] visit [to Pontiac, Michigan, in 1834], he came to our house. My heart swelled with love as I selected and presented him with some of our choice apples. While looking over our copy of a large English Book of Martyrs [by John Foxe], he expressed sympathy for the Christian martyrs and a hope for their salvation. He asked to borrow the book, promising to return it when he should meet us again in Missouri. On returning it he said, ‘I have, by the aid of the Urim and Thummim [Seer Stone?], seen those martyrs. They were honest, devoted followers of Christ, according to the light they possessed. They will be saved.’”
(In Hyrum L. Andrus and Helen Mae Andrus, comps., They Knew the Prophet: Personal Accounts from over 100 People Who Knew Joseph Smith , 83.)