Trump shooter Thomas Crook's cell phone seen on roof next to mystery device

The cell phone of Thomas Matthew Crooks, who shot Donald Trump at a Pennsylvania rally, has been found on the roof where he was positioned along with a transmitter, raising more questions as police continue to investigate.

Former President Donald Trump suffered a shot to his right ear as Crooks, 20, opened fire on the crowd in Butler on Saturday evening.

Three other attendees were also shot, including Corey Comperatore, 50, who died, and David Dutch, 57, and James Copenhaver, 74, who were seriously injured.

Crooks was subsequently shot dead by Secret Service agents. The transmitter has raised questions of whether the suspect was communicating with a partner in crime, and if the shooting was the only plan to disrupt the rally.

According to Channel 11′s Nicole Ford, law enforcement agents saw Crooks acting suspiciously outside the building from which he shot the ex-President over an hour before he pulled the trigger at 6.11pm.

The transmitter has prompted concerns that Crooks may have been planning to continue his killing spree if he had escaped from the roof with his life, and may have had an accomplice to help him.

Hours before the shooting, Crooks had asked for the day off, claiming he had "something to do".

Secret Service director Kimberly Cheatle was heavily questioned when official statements contradicted her previous claims that a Beaver County sniper team was stationed in the very building from which Trump was shot.

According to official reports, Crooks gained access to the security area of the rally three hours before the attack.

Witnesses told Channel 11 that the shooter was on the roof with his weapon for less than seven minutes before being confronted by a Butler Township police officer.

In his parents' house, where Crooks lived, authorities found a bulletproof vest and a third remote-controlled bomb.