Within hours of the Navy Yard shootings, the FBI had traced the gunman's recent shotgun purchase and sent agents to the shop in northern Virginia where he bought it.
Left out of the loop was the Bureau of Alcohol, Tobacco, Firearms and Explosives, a surprising snub between top U.S. law enforcement agencies that comes as the ATF struggles to show its relevance in Washington.
The ATF is the federal agency in charge of tracing guns used in crimes, including the military-style semi-automatic rifle used in rampage at a Connecticut school last year, a similar rifle used in the deadly shooting at a Colorado movie theater and a handgun used to kill six people and critically wound a congresswoman, among others, outside a grocery store in Tucson, Ariz.
By the afternoon of the Navy Yard shootings, FBI agents -- not ATF agents -- were in northern Virginia at the gun shop where Aaron Alexis, 34, bought a Remington 870 Express shotgun and about two dozen shells barely 48 hours earlier. By day's end it was clear that the shotgun, which Alexis altered with a sawed-down barrel and shoulder stock, was purchased legally after Alexis showed his valid Texas driver's license and passed both a state and federal background check.
But the ATF wasn't involved.
There is no evidence that the FBI did anything wrong in tracing the gun on its own, but the move is unusual.
"I have never seen an instance where ATF had not been relied upon to trace the gun," said Mike Bouchard, a former ATF assistant director for field operations. "I have never heard of a situation like that."
By 6 p.m. Monday, the day of the shooting, The Associated Press had learned that the shotgun had been legally purchased at a gun shop in Lorton, Va. When asked about those details, the ATF said its trace had not been completed. ATF spokeswoman Ginger Colbrun said in a statement Friday that once ATF traced the shotgun, that information was handed off to the FBI, which is leading the investigation. She declined to say when the ATF completed its trace.
"ATF is the sole federal agency that is authorized to conduct firearms tracing," Colbrun said in the statement. The ATF's National Tracing Center "is authorized to trace a firearm for a law enforcement agency involved in a bona fide criminal investigation."
The FBI's Washington Field Office declined to comment on the investigation.
A 1968 overhaul of gun laws gave the ATF the authority to trace firearms used in crimes and required that gun dealers keep records of who bought what gun and when. The powerful gun lobby has successfully pushed a series of legislation that limits what the ATF can do with that information, including bans on storing it in any searchable computer database.
When law enforcement needs to trace a gun, the low-tech process includes a series of phone calls, starting with the manufacturer. Depending on the age of the gun and how many times it has changed hands, the process can take days. In the case of the Navy Yard shotgun, Alexis bought the weapon just two days earlier. The paper trail ended about 17 miles from the crime scene.
The Navy Yard shooting comes less than three weeks after ATF Director B. Todd Jones was sworn in as the first Senate-confirmed ATF director.
The agency had been without a permanent leader since 2006 when the Senate was given the power to approve the director. In pushing for Jones' approval, Senate supporters, including President Barack Obama, suggested ATF was unnecessarily weakened by lack of leadership.
The ATF was noticeably absent in the gun debate that dominated the attention of lawmakers in the months after the December massacre of 20 school children and six adults at a Newtown, Conn., elementary school.
Bouchard said another law enforcement agency asking for gun sales records could be confusing for licensed dealers who have become accustomed to dealing with the ATF.
"Gun dealers are accustomed to dealing with ATF and will always be cooperative with any law enforcement agency," Bouchard said.
"But because of dealing with ATF there could be some confusion on their part as to what they have to do during an investigation, or if they should surrender records that they are legally instructed to keep by ATF."