The Federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) analysis has not conclusively determined that a bullet fragment removed during the autopsy of Charlie Kirk is related to the rifle found near the murder scene - the FBI is conducting additional tests, Tyler Robinson's defense lawyers said in recent court filings.

In court filings, Robinson's defense team has also requested a postponement of the preliminary hearing, which is scheduled for May, because they need time to review the bullet analysis, as well as an enormous amount of other material that may help exonerate the suspect.

The ATF bullet analysis report remains confidential, but lawyers have cited excerpts in other public documents that say the results were inconclusive.

The success of natural ballistic analysis depends largely on the size and condition of bullet fragments. Experts look for unique, microscopic markings that remain on a bullet as it passes through a gun barrel. Scratches are similar to fingerprints in that no two guns leave identical marks.

The defense side has said in its motion that they may try to use the analysis to exonerate Robinson at the preliminary hearing, while prosecutors aim to show they have enough evidence against him to proceed to trial.

Prosecutors intend to seek the death penalty for 22-year-old Robinson, who is charged with the September 10 murder of Kirk on the campus of Utah Valley University in Orem. Robinson has not yet entered a plea.

Prosecutors say Robinson's DNA was a match on the rifle's trigger, a spent bullet casing, and two unspent bullets. Defense attorneys note that autopsy reports indicate multiple people's DNA were found on some items, saying that requires more complex analysis.

Prosecutors say Robinson sent a message to his romantic partner saying he had "enough of hating" Kirk and chose him intentionally.

Robinson is back in court on April 17 to discuss the defense motion to ban cameras in the courtroom.