Crooks, 20, was shot and killed by Secret Service agents at a rally in Butler, where Trump is under intense scrutiny over whether he took protective measures.
Kimberly Cheatle, director of the Secret Service, was subpoenaed to testify before a U.S. House committee on July 22.
As first reported by The Wall Street Journal, investigators told CBS they were still trying to figure out exactly when Crook was piloting the drone.
They said they believed it had been just days since the rally at the Butler Farm Showgrounds.
Other US media outlets also cited security officials as claiming that the device was flown over the area on the day of the incident.
The drone is believed to have been used by the perpetrator to get the best view of the podium where President Trump will speak.
Crooks fired several shots from the roof of a building about 130 meters (430 feet) away from Trump.
In an interview with Fox News that will air in full on Monday, Trump said no one warned him there was a potential shooter before he went on stage.
“How did someone get up on that roof? And why wasn't he reported? Because people saw him up on that roof,” he said.
A drone found in the gunman's vehicle after the attack is currently being examined by investigators.
Two explosive devices, a tactical vest and four magazines filled with the same ammunition used in the attack were found in the suspect's vehicle.
