ATF: Smuggler Smuggled ICE Agent Murder Weapon “Prior to law enforcement’s awareness of the purchase”

From the ATF press release:

According to the court documents, at the meeting, two men unloaded several large bags containing firearms into the CI’s vehicle, which was kept under surveillance until a traffic stop in Laredo. According to the court documents, the two men’s vehicle was later stopped by local police and the men were identified as Ranferi and Otilio Osorio. Morrison was the third passenger in the vehicle. The vehicle stopped in Laredo was searched and 40 firearms, all with obliterated serial numbers, were seized . . .

Trace results indicated that three of these firearms could be specifically traced to Morrison, who bought them from federal firearms licensees (FFL) in the Dallas/Fort Worth area on Nov. 4, 2010. The investigation now has also revealed that on Aug. 7, 2010, a Romarm, model WASR, 7.62 caliber rifle was discovered by law enforcement officers in LaPryor, Texas, near the U.S./Mexico border. Trace results indicated that Morrison purchased this firearm on July 30, 2010, from a FFL. According to the affidavit, between July 10, 2010, and Nov. 4, 2010, Morrison purchased 24 firearms from FFLs.

In addition, according to one affidavit filed in the case, one of the three firearms used in the Feb. 15, 2011, deadly assault of ICE Special Agent Jaime Zapata that was seized by Mexican officials has been traced by ATF to Otilio Osorio. Otilio Osorio allegedly purchased that firearm on Oct.10, 2010, in the Dallas/Fort Worth metroplex, prior to law enforcement’s awareness of the purchase. Ballistic testing conducted by Mexican authorities on this firearm indicated it was one of the three firearms used during the deadly assault on Special Agent Zapata’s vehicle.

I’m having some trouble understanding this, and the ATF isn’t returning my calls. Let me see if I’ve got this straight. The ATF didn’t know about the smuggled guns that were used to kill U.S. Border Patrol Agent Brian Terry and ICE Special Agent Jaime Zapata before the murders, and yet they arrested the straw purchasers within hours of both crimes. Both of whom were already under their watchful eye. How does that work?