Susan Riehl knew her son was mentally ill, was off his medications and could be dangerous, so she took a reasonable precaution: She confiscated his many guns.

But just months before Matthew Riehl opened fire on Douglas County sheriff’s deputies at his Highlands Ranch apartment, killing one officer and wounding six other people on Dec. 31, his mother reluctantly returned the weapons because he threatened to sue her if she didn’t.

The legal battle between mother and son was revealed in hundreds of emails released by the University of Wyoming after The Denver Post filed a request for communications related to Riehl and threats to the law school from which he graduated in 2010.

Riehl had legally bought at least nine guns in Wyoming, and he claimed to have obtained 1,000 rounds of ammunition. Douglas County sheriff’s officials say Riehl used four guns — an M16 rifle, an M4 rifle, a shotgun and a Glock pistol — and fired 100 rounds during the shootout.

Susan Riehl took her son’s guns after the Veterans Administration detained Riehl in 2014 on a mental health hold, four years after he served in the Wyoming National Guard during a deployment to Kuwait. He escaped from the hospital and was brought back on a 72-hour involuntary hold. Veterans Affairs records contain other references to attempts at mental health treatment in the following years.

But her son, who became increasingly unstable and belligerent as the months and years wore on, berated his mother in a series of angry emails and demanded that she return his guns. He gave her a Sept. 9 deadline.

“If you do not return my property I will sue you for it and you will have to hire a lawyer who will tell you to return it annyway (sic),” he wrote on Aug. 24. “Try to behave like an adult for once in your life and reply by 9/9 or I will be initiating legal action against you.”

In another email, Riehl itemized all the things he said his mother took or tried to take from him: books, dog, friends, guns, car, house and freedom. “What type of mother would take everything from her son? Admit it, you hate me,” Riehl wrote.

Phone calls left for Susan Riehl, 71, of Lone Tree, were not returned. A man who answered her phone said, “We’re not talking to any media people so no, she’s not here.”

Helen H. Richardson, The Denver Post Elizabeth police officer Sean Bigler, middle, gets a hug from a fellow officer during a candle light vigil for her their friend and fellow officer Douglas County deputy sheriff Zackari Parrish at Mission Hills church on Jan. 1, 2018 in Littleton.

Helen H. Richardson, The Denver Post Officers and friends of slain Douglas County deputy sheriff Zackari Parrish hug one another during a candlelight vigil at Mission Hills church on Jan. 1, 2018 in Littleton.

Helen H. Richardson, The Denver Post Elizabeth police officer Sean Bigler, middle, cries with his wife and fellow officers by his side during a candle light vigil for his friend and fellow officer Douglas County deputy sheriff Zackari Parrish at Mission Hills church on Jan. 1, 2018 in Littleton.



Helen H. Richardson, The Denver Post Gracie Parrish, middle, holding her daughter Evie, rests her head in her hands, as she is overcome with emotion during a candlelight vigil for her slain husband Douglas County deputy sheriff Zackari Parrish at Mission Hills church on Jan. 1, 2018 in Littleton.

Helen H. Richardson, The Denver Post Douglas county sheriff deputies arrive for a candlelight vigil for slain Douglas County deputy sheriff Zackari Parrish at Mission Hills church on Jan. 1, 2018 in Littleton.

Helen H. Richardson, The Denver Post Volunteer Kim Lundquist, left, hands out candles before a candlelight vigil for slain Douglas County deputy sheriff Zackari Parrish at Mission Hills church on Jan. 1, 2018 in Littleton.



Helen H. Richardson, The Denver Post A Castle Rock police officer, wearing black over his badge, arrives for a candlelight vigil for slain Douglas County deputy sheriff Zackari Parrish at Mission Hills church on Jan. 1, 2018 in Littleton.

Helen H. Richardson, The Denver Post A makeshift memorial has started as people leave flowers on a police cruiser outside of the Douglas County Sheriff Substation for Deputy sheriff Zackari Parrish Parrish on Jan. 1, 2018 in Highlands Ranch.

Helen H. Richardson, The Denver Post People leave flowers on a police cruiser outside of the Douglas County Sheriff Substation for Deputy sheriff Zackari Parrish on Jan. 1, 2018 in Highlands Ranch. Parrish, 29, killed when deputies responded to a domestic disturbance at Copper Canyon apartment complex.



Helen H. Richardson, The Denver Post People embrace after leaving flowers on a police cruiser outside of the Douglas County Sheriff Substation for Deputy sheriff Zackari Parrish on Jan. 1, 2018 in Highlands Ranch.

Helen H. Richardson, The Denver Post Neighbors of Deputy Zackari Parrish placed blue ribbons on trees in honor of him on Dec. 31, 2017 in Highlands Ranch.

Helen H. Richardson, The Denver Post Sheriff deputies put up police tape around the scene of an early morning shootout that led to the death of a Douglas County sheriff deputy on Dec. 31, 2017 in Highlands Ranch.



Joe Amon, The Denver Post A gunman killed one Douglas County deputy and wounded four others during an early morning ambush as they responded to a domestic disturbance call at a Highlands Ranch apartment complex Dec. 31, 2017.

Helen H. Richardson, The Denver Post Police investigate the scene of an early morning shootout that led to the death of a Douglas County sheriff deputy on Dec. 31, 2017 in Highlands Ranch.

Helen H. Richardson, The Denver Post A tow truck driver secures the suspect's vehicle to his truck as police continue to investigate the scene of an early morning shootout that led to the death of a Douglas County sheriff deputy on Dec. 31, 2017 in Highlands Ranch. Deputy Zackari Parrish, 29, was killed and four other deputies were wounded in what police described as an ambush when deputies responded to a domestic disturbance at Copper Canyon Apartment complex at 3401 E. County Line Road.



Helen H. Richardson, The Denver Post Police investigate the scene of an early morning shootout that led to the death of a Douglas County sheriff deputy on Dec. 31, 2017 in Highlands Ranch. Deputy Zackari Parrish, 29, was killed and four other deputies were wounded in what police described as an ambush when deputies responded to a domestic disturbance at Copper Canyon Apartment complex at 3401 E. County Line Road.

Helen H. Richardson, The Denver Post Police investigate the scene of an early morning shootout that led to the death of a Douglas County sheriff deputy on Dec. 31, 2017 in Highlands Ranch.

Helen H. Richardson, The Denver Post Police investigate the scene of an early morning shootout that led to the death of a Douglas County sheriff deputy on Dec. 31, 2017 in Highlands Ranch.



Helen H. Richardson, The Denver Post Police investigate the scene of an early morning shootout that led to the death of a Douglas County sheriff deputy on Dec. 31, 2017 in Highlands Ranch.

Joe Amon, The Denver Post A gunman killed one Douglas County deputy and wounded four others during an early morning ambush as they responded to a domestic disturbance call at a Highlands Ranch apartment complex Dec. 31, 2017.

Joe Amon, The Denver Post A gunman killed one Douglas County deputy and wounded four others during an early morning ambush as they responded to a domestic disturbance call at a Highlands Ranch apartment complex Dec. 31, 2017.



Helen H. Richardson, The Denver Post Police investigate the scene of an early morning shootout that led to the death of a Douglas County sheriff deputy on Dec. 31, 2017 in Highlands Ranch. Deputy Zackari Parrish, 29, was killed and four other deputies were wounded in what police described as an ambush when deputies responded to a domestic disturbance at Copper Canyon Apartment complex at 3401 E. County Line Road. The gunman used a rifle and fired at least 100 rounds at the deputies. The gunman was killed in the shootout with law enforcement officers. Parrish is survived by a wife and two children. He had been a deputy for only 7 months. The other injured officers are Dep. Mike Doyle, 28, Dep. Taylor Davis, 30 and Dep. Jeffrey Pelle, 32. Castle Rock police officer Tom O'Donnell, 41 was also injured. All are listed as stable at area hospitals.

Joe Amon, The Denver Post A gunman killed one Douglas County deputy and wounded four others during an early morning ambush as they responded to a domestic disturbance call at a Highlands Ranch apartment complex. Dec. 31, 2017 in Denver.

Joe Amon, The Denver Post A gunman killed one Douglas County deputy and wounded four others during an early morning ambush as they responded to a domestic disturbance call at a Highlands Ranch apartment complex Dec. 31, 2017.



John Leyba, The Denver Post Police officers line up their patrol cars outside of Littleton Adventist Hospital for a procession honoring an officer who was fatally wounded in a domestic incident in a Highlands Ranch apartment complex on Sunday, Dec. 31, 2017.

John Leyba, The Denver Post Emergency personnel shield the cameras with a white sheet as they load fallen officer who was shot and killed during a domestic violence call in a Highlands Ranch apartment complex early Sunday. Various police agencies lined up for a procession for fallen officer on Dec. 31, 2017 in Littleton.

John Leyba, The Denver Post A bystander stands on the side of the road on S. Broadway holding an American flag as a procession leaves Littleton Hospital with fallen officer who was shot and killed during a domestic violence call in a Highlands Ranch apartment complex early Sunday. Various police agencies lined up for the procession on Dec. 31, 2017 in Littleton.



John Leyba, The Denver Post A hearse arrives at Littleton Hospital as officers from various police agencies line up for a procession for fallen officer on Dec. 31, 2017 in Littleton. One Douglas County deputy died and four more wounded along with two civilians Sunday morning at a Highlands Ranch apartment complex.

It’s unclear from the emails whether Susan Riehl returned the weapons by the September deadline, but she worried about what he might do once he had his guns, the emails show.

Between Oct. 30 and Nov. 21, Susan Riehl, law school administrators and police in Colorado and Wyoming exchanged a flurry of emails about Riehl and his deteriorating mental state. The emails show law school professors and administrators feared an imminent attack.

Riehl graduated from law school in 2010 and began practicing law, but he surrendered his Wyoming law license in 2016 and moved to Highlands Ranch.

The documents released by the university suggest students and professors had labeled Riehl unstable as far back as 2009 when a law student advisory council concluded he was “not suitable” for the law school.

“Matt was always unstable. I had run-ins with him as part of Board of Advocates, though as a legal research student he never approached me and I was not wary of him at the time,” interim law library director Debora Person, wrote in a Nov. 6 email to law school administrators.

By the end of October, Riehl unleashed hundreds of emails and social media posts against the university that included veiled threats.

Professors who received the disjointed emails from Riehl last fall urged him to seek mental health treatment. “Have you considered seeking a therapist? Seems like there’s more at play here. Make sure you’re taking care of your mental health,” one professor wrote.

On Nov. 5, several emails were exchanged by law school professors and administrators. That was the day Devin Patrick Kelley attacked a church in Texas, killing 26 and wounding 20. Using the name Matt Gonzo, Riehl posted a map of the church where the shootings happened.

“My phone is blowing up again tonight with notifications from Matt Riehl harassing the College of Law via social media, again,” law school spokeswoman Christine Reed wrote to dean Klint Alexander. “Frankly the level of harassment is starting to escalate and worry me.”

One professor urged the university to plan a drill “in the event of a situation.”

“I think we could all do with an egress refresher. I don’t think this is an unreasonable training request given the current status of our country. … (Riehl) is causing serious damage to our reputation as a law school and making it extremely difficult to do our jobs with any semblance of safety. … I think we need to be proactive about informing and protecting everyone.”

On Nov. 6, Sharon Wilkinson, executive director of the Wyoming State Bar, sent a message to Alexander with photographs of Riehl’s assault rifles. “His current mental state, combined with the high possibility that he has these in his possession are obviously extremely concerning,” Wilkinson wrote.

Also on Nov. 6, Lindsay Hoyt, assistant dean of the law school, sent an email to all law faculty and staff warning them about Riehl. The message included photographs of Riehl and his car. University staff were told to report any sightings “ASAP.”

Susan Riehl called university police officer Ira Werger on Nov. 7 and told him her son had stopped going to the VA, wasn’t taking his medications for bipolar and post-traumatic stress disorders and could be dangerous. She also forwarded emails from her son to Werger, but urged him to ignore them because “Matthew is not mentally well.”

Werger sent Matthew Riehl an email on Nov. 7 asking him for information about any misconduct he experienced at the law school. There was no reply by Riehl among the emails provided by the law school. The next day Werger contacted a law enforcement officer itemizing the 11 reasons why authorities needed to find Riehl.

Four of the reasons had been provided by Susan Riehl, including the fact that her son was armed and could be dangerous.

“I believe Matthew Riehl is a danger to himself or others and needs to be located in order to perform a welfare check for his own health and safety,” Werger wrote.

The name of the recipient of the email was redacted, but university police chief Michael Samp said his office sent warnings to Colorado officials about Riehl after learning he had moved to Douglas County.

On Nov. 21, Lone Tree Police Cpl. Michael Wagner emailed university police after writing Riehl a speeding ticket. He said Lone Tree police followed up and went to Riehl’s apartment.

“They found him at the address. While he didn’t let them in, he did speak with the officers. As of now we haven’t had any additional suspicious behavior. We are in a holding pattern,” the email says. “We did prepare a metro-wide bulletin about Riehl. We have an officer safety alert for his address.”

On the morning of Dec. 31, Riehl ambushed officers who came to his apartment, killing sheriff’s Deputy Zackari Parrish, 29, and wounding four other law enforcement officers and two civilians. SWAT team members shot and killed Riehl later the same morning.