Before the final episode of The Case Against Adnan Syed airs on Sunday night, Vulture has an exclusive clip previewing filmmaker Amy Berg’s potentially explosive conclusion to the docuseries. In it, Syed’s lawyer C. Justin Brown discusses another part of the defense’s strategy — searching for DNA evidence that could exonerate Syed in the murder of Hae Min Lee.

As Brown notes in the clip, there were many pieces of evidence that were never tested for DNA in the case, including Lee’s fingernails and a liquor bottle and condom wrapper found at the crime scene. The prosecution instead relied almost solely on Jay Wilds’s testimony that Syed strangled Lee in her car and they buried her body later that day.

“It’s not disputed that Adnan was in contact with the victim,” Brown says while driving in Baltimore. “He’s her former boyfriend, they remained friends after the two split up, so it wouldn’t be at all surprising if his DNA were in her car, so we have been and we will continue to be really careful about DNA testing.”

The clip comes just after Brown announced Thursday on Twitter that, “Recovered evidence in #AdnanSyed case was tested for DNA in the fall of 2018 and NOTHING was matched to Syed. There is no forensic evidence linking him to this crime.”

Through a public information request for the DNA test, the Baltimore Sun found earlier this week that prosecutors did not find any of Syed’s DNA under Lee’s fingernails, in blood samples on her shirt, or anywhere else at the burial site. The only DNA recovered aside from Lee’s was from an unknown female. A spokesperson for the Maryland attorney general’s office told the Sun, “These results in no way exonerate him.”

“While these DNA results do not reveal the true killer, they do go a long way in showing that the wrong person is in prison,” Brown offered in the Sun report. Noting the prosecution’s theory that Syed overpowered and strangled Lee in close quarters, he added, “If such a struggle occurred, it seems likely that the assailant’s DNA would have been present under the victim’s fingernails, or somewhere else inside the car. The recent testing, however, found none.”

It’s unclear how much else the fourth and final episode will reveal about DNA testing in the case made famous by Serial, though previews show it will cover the denial of Syed’s request for a new trial that happened earlier this month. It airs on HBO Sunday, March 31 at 9 p.m. ET.