David Bogdanov, 27, was convicted of second degree murder and malevolent harassment, according to Clark County Superior Court records.
Malicious harassment is Washington state’s hate crime law.
Prosecutors say that when Bogdanov found out that Nikki was biologically male, he got angry and killed her.
The 17-year-old was missing in June 2019 and her remains were found six months later in a heavily forested area of Larch Mountain near Vancouver, Washington.
Social media and phone recordings led police to Bogdanov, who had communicated with Nikki on Snapchat the day she disappeared.
Bogdanov testified in his own defense on Tuesday, admitting he killed her but said he did it in self-defense, a claim that prosecutors refuted, CNN subsidiary KATU reported.
At the time of Bogdanov’s arrest, Vancouver police officer Lt. Tom Ryan told reporters that the man picked up the victim in a van and took him to an apartment.
There the teenager confirmed that she was biologically male and Bogdanov made a statement “that he was really, really uncomfortable and bothered, and he asked Nikki to get out of his van and she walked away,” Ryan said.
In the stands, he said the teen fought him and grabbed a gun and said he had no choice but to subdue her, KATU reported.
Court documents suggest that Bogdanov strangled the teenager with string, according to KATU.
Bogdanov admitted that he dumped the girl’s body near Larch Mountain in remote Clark County in June 2019, according to KATU.
When questioned, he admitted that he would have found it “humiliating” if his family found out he was with a transgender woman.
The verdict is scheduled for September 9th.
CNN’s Andy Rose also contributed to this story.