FILE - This 2017 file photo provided by Xinyang Zhang shows his sister, Yingying, with their parents, Ronggao Zhang, right, and Lifeng Ye, at a train station in Nanping, China. The 26-year-old visiting scholar at the University of Illinois at Urbana-Champaign, disappeared June 9, 2017. Brendt Christensen, a former graduate student, has been charged with kidnapping and killing her. Zhang's body has not been found.  (Xinyang Zhang via AP, File)

PEORIA, Ill. (AP) — A former University of Illinois doctoral student on trial in the killing of a visiting scholar from China bought Drano and garbage bags three days after the slaying, according to testimony Thursday.

The detail came during the second day of the federal murder trial of Brendt Christensen in the June 2017 death of 26-year-old Yingying Zhang.

During opening statements Wednesday, a federal prosecutor, Eugene Miller, told jurors in grisly detail what authorities believe happened to Zhang. Miller said Christensen took Zhang to his apartment and raped, choked and stabbed her in his bedroom. Miller said Christensen then dragged Zhang into his bathroom and pummeled her in the head with a baseball bat before decapitating her.

It wasn't immediately clear what Christensen is alleged to have done with the garbage bags — or the Drano. The liquid commonly used for unclogging sinks, tubs and other drains contains sodium hydroxide or lye, which can be used for dissolving organic matter.

The (Champaign) News-Gazette reported that an FBI agent testified about the massive search in Illinois for Zhang that extended from local parks to a coal mine 30 miles (48 kilometers) away but didn't produce any evidence of what happened to her. She's never been found and is presumed dead.

Authorities say Christensen posed as an undercover officer to lure Zhang into his car on June 9, 2017, as she was on her way to sign a lease off campus in Urbana, 140 miles (225 kilometers) southwest of Chicago.

FBI Special Agent Anthony Manganaro testified Thursday about how he and University of Illinois detective Eric Stiverson tried to pin down Christensen about his whereabouts and actions on the day Zhang disappeared.

Manganaro said Christensen's story kept changing during questioning. Video of the interview played for jurors shows Christensen repeating his earlier claim he'd been sleeping or playing video games at home at the time Zhang was seen on surveillance video getting into a black Saturn Astra.

After initially noting he wasn't seen in the video of him picking up Zhang, Christensen says, "Maybe I'm getting my days mixed up. I did pick up a girl."

Special Agent Joel Smith testified Christensen was identified as a person of interest from a list of owners of Saturn Astras, which he said is a fairly uncommon vehicle. Christensen's Astra had a sunroof and a cracked hub cap, which were seen in the video.

Manganaro also testified that based on Christensen's Google searches, the defendant kept close tabs on news coverage of Zhang's disappearance.

Christensen was arrested on June 30, 2017, his birthday, after his girlfriend wore a wire for the FBI in an attempt to capture incriminating statements by Christensen.

It's the first federal death-penalty case in Illinois since the state struck capital punishment from its books on grounds death-penalty processes were too error-prone.

The trial was moved to Peoria in central Illinois after Christensen's lawyers said pretrial publicity would have made it impossible for the 29-year-old former physics student to get a fair trial in the Champaign area, where the 45,000-student university is located.

Thursday's testimony came a day after defense attorneys, hoping to spare Christensen the death penalty, acknowledged he killed Zhang.

FILE - This 2016 selfie provided by her family shows Yingying Zhang in a cap and gown for her graduate degree in environmental engineering from Peking University Shenzhen Graduate School. The 26-year-old visiting scholar at the University of Illinois at Urbana-Champaign, disappeared June 9, 2017. Brendt Christensen, a former graduate student, has been charged with kidnapping and killing her. Zhang's body has not been found. (Zhang Family Photo via AP, File)
FILE - This photo provided by the Macon County Sheriff's Office in Decatur, Ill., shows Brendt Christensen. Jury selection starts Monday, June 3, 2019 in Peoria, Ill., for the federal trial of Christensen in the 2017 disappearance and suspected killing of Yingying Zhang, a visiting scholar from China whose body hasn’t been found.  (Macon County Sheriff's Office via AP, File)
Members of visiting University of Illinois scholar Yingying Zhang's family walk with lawyers outside of the Federal Building and U.S. Courthouse Wednesday, June 12, 2019, in Peoria, Ill., before the trial of Brendt Christensen. (Stephen Haas/The News-Gazette via AP)
Defense attorney Julie Brain walks outside of the Federal Building and U.S. Courthouse Wednesday, June 12, 2019, in Peoria, Ill., before the trial of Brendt Christensen. (Stephen Haas/The News-Gazette via AP)