ST. THOMAS — Federal investigators have used ballistic technology to link a firearm found in Hospital Ground on April 8 with the murder of Deshaune Harrigan earlier that day, according to documents filed in U.S. District Court.

The development came in an affidavit filed by a special agent with the Bureau of Alcohol Tobacco and Firearms on Aug. 26 for the arrest of Romeo Walter, which was unsealed Friday.

Walter was apprehended Thursday during a traffic stop in Oklahoma and was charged with being a felon in possession of a firearm, possession of a firearm with an obliterated serial number, possession of a firearm in a school zone, and two related local charges, according to a news release from U.S. Attorney Gretchen Shappert.

Walter is the fourth person to be charged in connection with a cache of weapons found on April 8, while police were investigating homicides in Hospital Ground.

While out walking in the area, officers encountered several men who fled, according to court records. Police cornered 32-year-old Kenan Thomas and charged him with possession of four illegal weapons, and investigators found surveillance video from a nearby home that shed more light on the crime.

The video shows Thomas, Nijohntea Walker and Dijhani Julien apparently stashing a gun in a black duffel bag that was later recovered during Thomas’s arrest, according to court records.

Inside the duffel bag, officers found four weapons — a “Serbian Zastava AK-type pistol, 7.62 mm with an obliterated serial number,” an American Tactical AR-type pistol, a Glock .45-caliber handgun, a Glock 10 mm handgun, multiple magazines,” and two cellphones, according to court records.

Prosecutors said the surveillance video also shows Walker later returning to the area to retrieve a Glock-style pistol while Julien acted as lookout, and that weapon has not been recovered.

The video also shows a fourth man, Walter, who was wearing a sling, according to court records.

At around 8 p.m. the same day, officers investigating the death of Michael Mckie interviewed witnesses who said they saw three men leaving the scene, and one “had a medical sling around his arm similar to that seen worn by Walter in the video surveillance.”

Julien and Walter purchased one-way airline tickets off St. Thomas, and Julien was arrested on April 19 at King Airport while trying to board the flight, according to the court records. “With him at the airport, also with a one-way ticket, was Romeo Walter.”

Officers recovered shell casings at the scene of each murder, and “those casings are of the same caliber of weapon found inside the black back pack style bag that the defendant possessed in the video,” according to court records.

On May 22, the shell casings from the scene of Harrigan’s murder were matched “to spent shell casings test-fired from the Serbian Zastava AK-type pistol found in the black back recovered in the possession of Kenan Thomas,” according to the ATF affidavit for Walter’s arrest. “The firearm and spent shell casings from the murder scene are currently at the ATF laboratory for microscopic comparison and link confirmation.”

On Aug. 12, DNA analysis of swabs taken from the objects found in Thomas’s possession confirmed that Walter’s DNA “was conclusively found on the following items: the black bag containing the firearms and ammunition; the Glock 20 10 mm pistol; the Glock 21 .45 caliber pistol; and two AK pistol magazines,” according to the affidavit.

The special agent reviewed Walter’s criminal history and found he has three felony convictions in Maricopa County, Ariz., including two from 2012 — aggravated assault and abuse of a child or vulnerable adult — and possession of marijuana in 2017.

Walter is not permitted to carry firearms because of his felony convictions.

“I believe that Romeo Walter was in possession of multiple firearms and ammunition, one of which is suspected to have been used in a murder of Harrigan earlier the same day,” the ATF agent wrote in the affidavit.

The ATF has issued a $15,000 reward for information about the recent string of homicides in Hospital Ground that left Harrigan, McKie and Junior Freeman dead in early April.

To report information about the homicides, call 911, call or text the ATF directly and anonymously at 202-702-7219, or the anonymous tip service Crime Stoppers USVI at 1-800-222-8477.

— Contact Suzanne Carlson at 340-714-9122 or email scarlson@dailynews.vi.