What specific evidence did the FBI cite in concluding the shooter acted alone in the Butler, Pennsylvania attack?
Executive summary
The FBI grounded its conclusion that Thomas Matthew Crooks acted alone on a convergence of physical-scene forensics, chain-of-fire accounting, digital-device exploitation, exhaustive interviews at home and abroad, and international cooperation that found no foreign coordination; bureau officials also emphasized that every spent round was accounted for and that items from the roof (weapon, shell casings, biological samples, photos) were collected and sent for lab analysis [1] [2]. The agency repeatedly framed its finding as contingent—there was no evidence of co-conspirators in the material it examined, but investigators said the probe would reopen if credible new information surfaced [3] [1].
1. Physical forensics and scene processing: the roof as a sealed evidentiary locus
FBI spokespeople described a meticulous evidence collection on the roof where the shooter fired, with evidence response teams securing and photographing the scene, retrieving the firearm, shell casings, biological samples and other items before any cleanup, then transporting key items—specifically the shooter’s weapon and cellular phone—to the Quantico lab for processing [2] [1]. That chain of custody and subsequent lab work underpinned the bureau’s confidence that physical traces linked to the shooter alone accounted for the ballistic and biological footprint at the site [1].
2. Ballistics and “no phantom rounds”: accounting for every shot
Officials repeatedly stressed that investigators could account for every round fired at the rally and that there were no “phantom rounds” or unexplained trajectories; the bureau explicitly dispelled theories of a second shooter by matching casings and impacts to a single shooter and noting that a person observed near a water tower was a Pennsylvania State Police officer, not an additional gunman [2] [4]. That one-to-one mapping of spent brass and impact sites informed the conclusion that a single firearm and operator produced all wounds and strikes at the scene [2].
3. Digital exploitation and international checks: phones, accounts, and foreign leads
Investigators exploited the shooter’s digital devices—seizing his phone and other media—and pursued thousands of interviews and international requests to access foreign-registered email accounts, which the FBI said produced no evidence of ties to foreign individuals, governments or organizations and showed no sign of operational coordination in planning the attack [5] [2]. Agency leaders framed the international cooperation as exhaustive, noting that foreign accounts were fully accessed and yielded no coordinating communications linking Crooks to outside actors [5].
4. Interviews, manpower and the “lone planner” portrait
The bureau described an unprecedented manpower commitment—hundreds of agents and hundreds of interviews both domestic and foreign—to trace contacts and motives, concluding that Crooks had limited in-person and online interactions related to planning the attack, did not share intent with others, and therefore planned and executed the assault alone [6] [2]. Senior FBI officials portrayed the outcome as the product of broad canvassing rather than a narrow forensic read, saying thousands of interviews and reviews supported the lone-actor determination [2].
5. Open questions, dissenting voices and limits of available reporting
The FBI acknowledged that motive remains unclear in its public statements, and other outlets reported continuing questions about Crooks’s online footprint and ideological evolution—criticisms amplified by media figures who argue the bureau downplayed his digital activity—underscoring lingering debates about interpretation even if not about the lone-actor finding itself [7] [8]. Reporting available for this analysis is heavily sourced to FBI public remarks and a Fox News “exclusive” briefing with bureau leadership; those sources provide the specific pieces of evidence the bureau cites but also reflect the FBI’s framing and do not represent an independent forensic dossier reproduced here [2] [1].
6. Final posture: conditional closure, evidence-based claim, and willingness to reopen
While the FBI closed its investigation with the conclusion that Crooks acted alone and cited the combined physical, ballistic, digital and interview evidence summarized above, officials explicitly left the door open to reopen the probe should credible new information emerge, and media coverage records both the bureau’s evidentiary claims and public skepticism from critics who say questions remain about online activity and narrative control [3] [8].