The Capitol Hill shooter was caught on camera lying in wait for his victim before he murdered Ashli Babbitt of San Diego, California as she toured the United States Capitol Building in Washington, D.C. The video is embedded below. The shooter appears to be a white male in a black business suit with a handgun. Unfortunately, his face is not visible, but he does appear to have a widow's peak or pattern baldness, so he is probably at least 30 years old.
Lying in wait is defined as "to hide and wait for the right moment to make an attack" - Merriam Webster (https://www.merriam-webster.com/dictionary/lie%20in%20wait). The shooter, who is believed to be a Capitol Police officer, can be seen hiding behind a barricade in a doorway to the far left of Babbitt. He gives no warning or otherwise do anything to inform Babbitt, who was on the far right behind other people, that he was there. He just hid there and said nothing. She most likely tried to climb through the window on the right side of the door with no idea that there was an armed man in the doorway to the far left behind the barricade. Her killer clearly intended to kill anyone that came breached the door and had no intention of giving anyone notice let alone a warning that probably would have saved her life. Lying in wait is often used as an aggravating factor under various murder laws capable of elevating lesser killing to first degree murder because it proves premeditation.
Ashli Babbitt was a 35 year old Air Force veteran that served the country for 14 years. She was supporter of President Donald Trump and a believer in Q-Anon theory.