South Dakota prosecutors charged a Sioux Falls man on Monday with first-degree murder and aggravated eluding in the death of a deputy who was struck while putting out spikes during a police chase.

Joseph Gene Hoek, 40, was ordered held without bail at his first court appearance in the death of Moody County Chief Deputy Ken Prorok, 51, of Wentworth, who died during the pursuit on Friday.

The murder charge carries a maximum sentence of death or life without parole, officials said. 

People close to Hoek described him as being on a “downward spiral” marked by drug use and escalating threats of violence, Special Agent Jeffrey Kollars of the South Dakota Division of Criminal Investigation wrote in a court filing dated Sunday.

South Dakota Attorney General Marty Jackley is prosecuting the case himself. He said he still needs to investigate any mitigating factors, then sit down with Prorok’s family, and then with the sheriff and his deputies, before deciding whether to seek the death penalty.

“I believe the attorney general should lead from the front and I’ve always tried to do that,” Jackley told The Associated Press. “Especially when it involves a law enforcement officer that gave the ultimate sacrifice.”

Hoek’s attorney, Manuel De Castro, told AP his initial impression is that Hoek was “overcharged,” and that “there are some mental health issues that need to be explored.” But he said he’s still gathering information.

“I know it’s an emotional case for everybody involved. But we’ll go from there,” he said.

Kollars wrote that Madison police responded Friday afternoon to a call about a man, identified as Hoek, making “homicidal threats” near the business where the caller worked. Police spotted his car and tried to stop him, but Hoek sped off on Highway 34 toward Interstate 29, according to the agent.

The chase reached 115 mph. Prorok stopped to deploy stop spikes across Highway 34. But a witness said he saw the approaching car intentionally swerve and strike the chief deputy before it went into the ditch and flipped, the agent wrote. Hoek ran off on foot.

According to court documents, the witness tried to give Prorok first-aid until law enforcement could get there, CBS affiliate KELO-TV reported. Once officers arrived, the witness ran after Hoek and held him until authorities caught up.

“My heartfelt thank you to that witness. I know who you are, I appreciate what you did,” Moody County Sheriff Troy Wellman said, according to KELO.

Prorock died at the scene. Hoek was checked at a hospital but was not seriously hurt.

Kollars wrote that he interviewed Hoek after he waived his right to remain silent. The agent wrote that Hoek told him he had gone to the business to collect from the caller, who he said owed him money.

“When Hoek was told that a Deputy Sheriff was killed by his actions and decisions, he responded that he didn’t believe me,” the agent wrote. But Hoek had claimed that he has problems with anxiety and panic attacks that sometimes affect his memory, the agent said.

Investigators who searched the car found suspected THC vapes, suspected marijuana paraphernalia and “blunts,” and containers of cold medicine, the agent wrote. Outside the car they found an apparent bong and an unopened bottle of liquor, he said.

When asked about drugs, Hoek told authorities he suffered from pain and that he had obtained the prescription narcotic pain reliever hydrocodone on some emergency room visits. But he said many doctors denied him the medications he wanted. He said he had used medical marijuana for anxiety “days prior” and had been prescribed the anti-anxiety drug Xanax but couldn’t recall the last time he used it.

Hoek also said he had been kicked out of several relatives’ homes but did not specify why.

The person who called police told investigators Hoek had been a “family friend” who “started scaring him” and “started acting weird lately,” which led the person to obtain no-contact and no-trespass orders last month, the agent wrote.

Hoek’s mother told investigators that she believed her son “was suffering from mental health issues and was self-medicating,” but was smart enough to fool mental health professionals who evaluated him, so he would get released quickly with no help. She also said he was addicted to dextromethorphan, a cough medicine that is sometimes abused.

One person said Hoek’s “downward spiral” escalated after she obtained an order for protection against him last month and that he became “increasingly physically violent,” the agent wrote.

“These charges are based on the evidence including that set forth in the probable cause affidavit,” Jackley said in a statement. “Our thoughts and prayers remain with Chief Deputy Prorok’s family. I appreciate the diligent investigation conducted by the State Division of Criminal Investigation, the Highway Patrol, and local law enforcement agencies.”