A tree may have prevented one of the sniper teams tasked with protecting former President Donald Trump at his Pennsylvania campaign rally from clearly seeing the would-be assassin as he climbed on a roof and opened fire, according to a CBS News analysis of video and satellite imagery.

The tree, located between the shooter and the sniper team closest to him, may have impaired the team’s line of sight as the gunman climbed onto the roof from where he fired multiple rounds. That sniper team, which was positioned on a roof over Trump’s right shoulder, did not fire the shot that killed the gunman, two federal law enforcement officials told CBS News.

A U.S. Secret Service sniper stationed in a building behind the former president fired one round, killing the gunman, according to multiple law enforcement officials. Two federal law enforcement officers told CBS News the Secret Service team that ultimately killed the shooter was located on a building behind Trump’s left shoulder — with a view that was not blocked by the tree, the CBS analysis shows. That team was initially directed to go another way, so the snipers had to reorient themselves before taking down the gunman, CBS News’ Charlie de Mar reported.

The motive of gunman Thomas Matthew Crooks remains a mystery four days after the shooting at a rally in Butler, Pennsylvania — during which Trump and two others were injured and a rallygoer was killed. A federal law enforcement bulletin obtained by CBS News identified the gunman as “an apparent lone attacker” and the FBI is investigating whether he was a politically motivated homegrown domestic violent extremist.

Minutes before the assassination attempt, a sniper from a local tactical team took a photo of the gunman and saw him looking through a rangefinder, a local law enforcement officer with direct knowledge of the events told CBS News.  Cellphone video taken Saturday shows rally attendees pointing toward the shooter and trying to alert authorities to his presence — a full two minutes before the 20-year-old opened fire.

The U.S. Secret Service is facing mounting questions about the security flaws that allowed the shooter to fire from a rooftop near the rally. Meanwhile, House Republicans are ramping up efforts to investigate the attempted assassination.

President Biden said earlier this week that he is directing an independent review of security and events at the rally to determine what went wrong, while the Department of Homeland Security’s inspector general is opening an investigation into the rally’s planning.

Eric Trump, the former president’s son, told CBS News his father doesn’t have stitches after he was shot, but has a “nice flesh wound.” He said his father’s hearing is fine and that he is “in great spirits.”

With reporting from Erielle Delzer, Alex Clark, Rhona Tarrant and Kaia Hubbard