Police issued an alert for Darby on Monday asking the public to keep an eye out for him.
"We do not believe at this time that this was a random act of violence", Pittsburgh Police Chief Scott Schubert said, via WPXI.
Authorities said she died of head trauma, and the case was ruled a homicide.
"At this point, we are actively interviewing people in the area and canvassing the area looking for further information", Pittsburgh police Sgt. William Vollberg said.
Police and paramedics were first dispatched to the scene Sunday at 8:56 a.m. On Sept. 20, Sheykhet filed an application for a PFA against Darby for breaking into the second-floor window of the home she was renting on Cable Street in Oakland.
Weeks earlier, on September 26, Darby was arrested for breaking into Sheykhet's Cable Place residence, according to a Police statement.
The Russian student was found dead inside her home on Sunday morning by her father who broke down the door when she failed to answer calls.
Because of his absence, the DA is in the process of getting a judge to revoke Darby's bond, making him wanted by law enforcement in two counties. Her dad, exhausted of not finding a solution, in the long run broke down the entryway and saw the body, Sheykhet's sibling, Artem - who commended his 25th birthday celebration that day - told WPXI. Darby was a student at Pitt's Greensburg campus but withdrew from the University earlier this month, according to Pitt spokesperson Joe Miksch. Her roommates thought she was asleep.
"She didn't answer the phone". I pushed open the door and she was laying on the floor.
"Our grounds is disheartened and stretches out its most profound sensitivities to the understudy's family and the individuals who knew her", a Pitt representative said in an announcement. She was found on the floor.
Police said Mr Darby is potentially armed and unsafe. They became closer friends when they both attended Montour High School, and Smith said their friendship continued through college. He said those who knew her will miss her enthusiasm and ability to lighten everyone's mood.
She won a place at the university after graduating from a high school in Pittsburgh after relocating to the U.S. with her family from Ivanovo, Russia.
"I could go on and on about how much of a wonderful person she is", former classmate Mark Schlaegle told the Pittsburgh Post-Gazette.