A contractor says the suspected killer of University of Utah student Mackenzie Lueck asked for the construction of a sound-proof room in April, complete with hooks in the concrete walls and a fingerprint lock.

"He was adamant about getting it done really fast and money was no object," said contractor Brian Wolf, who turned down the job.

Ayoola Ajayi, 31, was arrested Friday and is expected to be charged with Lueck's murder. Police found remains matching Lueck's DNA in his backyard.

Police have also said that Ajayi was accused of rape five years ago in northern Utah, but the victim there declined to press charges.

Prosecutors are now reviewing evidence from police and the district attorney will decide whether to recommend the death penalty. Investigators spent the weekend gathering more evidence at the home of Ajayi.

"There is extensive investigation follow-up that needs to be done and we will proceed," Salt Lake City Police Chief Mike Brown said. "It's not over right now."

Days earlier, they found Lueck's charred remains and belongings in Ajayi's backyard. Police say there is currently no other "person of interest" in the case, but the investigation is pending.

"We want to know if he acted alone or if there were people that helped him along the way," Brown said.

Lueck was last seen on surveillance video at the Salt Lake City Airport two weeks ago. Investigators say they used phone location data to place both Ajayi and Lueck in the park where she was dropped off by a rideshare.

Lueck was a senior at the University of Utah, majoring in kinesiology. In an online post, her sorority sisters said they're reflecting on the "lasting impact she made on the lives of her family members, friends and sisters." A memorial has gone up on campus. Students will hold a vigil Monday night to honor their former classmate.

"This is just crazy, it's crazy, she didn't deserve it," Andrea Simpson, one of Lueck's neighbors, said. "Nobody deserves that, you know."

Ajayi describes himself online as an IT worker. Both Ajayi and Lueck had online dating profiles, but police have yet to say how the two initially connected.

Ajayi's attorney is declining to comment.