Arcan Cetin, the man charged with killing five people in a shooting at Cascade Mall in Burlington, Wash., last September was found dead Sunday night at the Snohomish County Jail.

The Skagit County Prosecutor's Office said Arcan Cetin (pronounced AR'-jahn CHEHT-in) was discovered hanging in his cell just before 9 p.m. The office could not immediately say why Cetin had been transferred from Skagit County.

Cetin, 20, was charged with five counts of aggravated first-degree murder for the Sept. 23, 2016, killings. The charges alleged Cetin acted with "premeditated intent" when he used a rifle to kill a teenage girl, three women and a man at the Macy's Women's store inside the mall, 65 miles north of Seattle.

Cetin's stepfather, David Marshall, previously told the media that Cetin "has had mental health issues that we have been working on him with."

The 20-year-old had a history of violent behavior toward his family and ex-girlfriend. His neighbor described Cetin as "creepy."

Cetin had visited his mother and Marshall before the Sept. 23 shooting, and stole his stepfather's .22-caliber Ruger rifle, which had been hidden under a bed, according to records acquired by The Associated Press.

On the night of the shooting, he first went to the mall's movie theater and used his cell phone to prop the door open when he went outside. But another movie-goer closed the door behind him and gave the phone to theater officials, thwarting whatever plans Cetin may have had.

Soon after, Cetin retrieved his phone from officials and went into the mall.

Cetin entered through the Chuck E. Cheese restaurant just before 7 p.m. and headed for the Macy's Women's store, Mount Vernon Police Officer Dave Shackleton said in an arrest warrant affidavit.

Surveillance video shows Cetin shooting a teenage girl near some clothing racks and then shooting a man. He then headed for the cosmetics section where he shot two women who were hugging and trembling in front of the counter and one who was trying to hide behind it.

Cetin left the rifle with a 25-round magazine on a cosmetics counter before fleeing, police said in court documents. The victims ranged from a 16-year-old girl to a woman in her 90s and included a probation officer and a Boeing maintenance worker.

Authorities circulated a photo of the shooter taken by a surveillance camera, and soon identified Cetin as that man.

He was arrested about 30 hours later as he walked near his apartment in Oak Harbor, Washington. He had been hiding in Seattle and sleeping in his car while on the run, records showed.

During interviews with police, Cetin admitted that he shot the five people at the mall, but did not provide a reason.