The federal bureau's top man's currently testifying in front of a Congressional Committee about the shooting that nearly claimed the former President's life ... and, he says the law enforcement agencies recovered three bombs, presumably set up by Crooks.

Check out the clip ... Wray says they found three total devices -- two in his car and one in his home -- all with the ability to be detonated remotely. There were receivers at the scene for two of the devices, and Crooks had a transmitter to detonate them.

However, Wray says because of the configuration of the on/off positions of the receivers, the devices probably wouldn't have exploded -- seemingly a testament to Crooks' inexperience in this area -- though that doesn't mean the explosives weren't dangerous.

Another revelation ... Wray says Crooks flew the drone recovered in his vehicle about 200 yards from the stage, possibly live streaming the flight -- and, getting a very close look at the surrounding area.

Worth noting ... he didn't fly the drone over the stage area, according to Wray -- but, it's still more evidence of the danger all the rally attendees were in and punctuates law enforcement's poor response to the incident.

As you already know ... the Secret Service spotted Crooks 20 minutes before he took his first shot at Donald Trump on the roof, but didn't take him down and Kimberly Cheatle -- the Secret Service director who's since resigned her post -- called the whole incident a massive operational failure.