SIOUX FALLS — Three South Dakota men with prior felony convictions will serve time in federal prison after pleading guilty to possessing firearms despite being barred from doing so, according to federal prosecutors.
A U.S. district judge sentenced Dominic Houston, 28, of Sioux Falls, to three years and four months in federal prison. Spencer Patterson, 23, also of Sioux Falls, and Chase Zephier, 28, of Yankton, each received sentences of two years and three months.
All three men were also ordered to serve three years of supervised release after completing their prison terms. The sentences resolve separate possession allegations tied to the same broader investigation, which began in April 2025.
Case began with ammunition purchase
Federal prosecutors said an off-duty Sioux Falls police officer saw the three men buying ammunition at a Sioux Falls retailer on April 21, 2025. The officer recognized one of the men and knew that person had a felony conviction that prohibited possession of both firearms and ammunition.
The officer passed the information to on-duty police. Officers later tried to stop the vehicle connected to the men, but prosecutors said the vehicle fled and police chose not to pursue it.
Authorities located Houston and Zephier hours later during another traffic stop. A search of the vehicle produced two handguns, according to the prosecution’s account of the case.
| Defendant | Residence | Federal prison sentence |
|---|---|---|
| Dominic Houston | Sioux Falls | 3 years, 4 months |
| Spencer Patterson | Sioux Falls | 2 years, 3 months |
| Chase Zephier | Yankton | 2 years, 3 months |
Two pistols recovered from vehicle
Prosecutors said officers found a Glock 9mm handgun beneath Zephier’s seat. They also found a Glock .40-caliber pistol inside a bag that police had previously seen Houston wearing.
Zephier later acknowledged possessing the handgun found under his seat, according to the case information released by prosecutors. Houston’s DNA was found on the second pistol, prosecutors said.
Patterson was not in the vehicle when police stopped it. Investigators later obtained a search warrant for his home and recovered a Smith & Wesson .40-caliber pistol, according to federal prosecutors.
Federal prohibition applied to all three
The charges were based on the federal offense of possessing a firearm by a prohibited person. In this case, each defendant had previously been convicted of a felony, which prosecutors said prevented him from legally possessing firearms or ammunition.
The guilty pleas removed the need for a trial and left sentencing as the next major stage in the federal case. The prison terms imposed by the judge differed for Houston and the other two defendants, although Patterson and Zephier received identical sentences.
Prosecutor praises off-duty officer
U.S. Attorney Ron Parsons credited the off-duty Sioux Falls officer whose observation at the ammunition retailer set the investigation in motion.
“The incredible awareness and dedication of this off-duty Sioux Falls police officer almost certainly prevented additional crimes,” U.S. Attorney Ron Parsons said in a statement.
Parsons also characterized the defendants’ conduct as potentially connected to more serious plans, but the information released about the case does not identify any additional offense or describe a specific planned crime.
What supervised release means in the case
The three men will begin their supervised-release terms after leaving federal prison. The release periods are separate from the prison sentences and will extend for three years for each defendant.
The case illustrates how a police observation involving ammunition can lead to a wider firearms investigation. The initial attempted traffic stop did not result in a pursuit, but officers later located two of the men and recovered weapons during a separate stop. A later residential search produced the firearm connected to Patterson.
The sentences also underscore the consequences of firearm possession for people with qualifying felony convictions. Prosecutors said the prohibition covered both guns and ammunition, making the ammunition purchase itself an important part of the investigation even before the pistols were recovered.
Houston, Patterson and Zephier will serve their sentences in federal custody, followed by the supervised-release periods ordered by the court. The federal case involved residents of Sioux Falls and Yankton and firearms recovered from both a vehicle and a home.
