WASHINGTON (CNN) -- Sources close to the investigation of last Friday's Capitol shooting say a security camera captured the man charged in the incident, Russell Weston Jr., shooting police officer Jacob Chestnut while moving through a metal detector.
The gunman, wearing a medium-brimmed, floppy hat, fired at Chestnut with his left hand. The next sequence shows him holding the weapon in his right hand before "contorting" as a result of being hit by shots from another Capitol Police officer, the source said.
The shooting of Capitol Police Detective John Gibson takes place further down the hall and is not shown on the tape.
The source, who has seen the tape, said it may take a few more days to analyze it. Officials are trying to determine whether Weston entered and left the building before the shooting, which would indicate premeditation.
Parents receive permission to visit Weston
Weston remains in serious condition at a Washington, D.C., hospital with gunshot wounds to the chest, an arm and a leg.
From their family home in Illinois, his parents told CNN that after repeated requests to the Washington Corrections Department, they have received permission to visit their son.
"We want to see him very bad, and we want to tell him face to face that we do love him and what he's done is horrible. But regardless, we still love him," said Russell Weston Sr.
The Westons said they don't know when they will arrive in Washington. Until now they've been sending messages to their son through his lawyer, public defender A.J. Kramer, and hospital nurses.
Insanity defense likely?
Weston's family says he was diagnosed as a paranoid schizophrenic but refused to take his medication. His lawyers have asked a judge to allow a psychologist and psychiatrist to visit Weston in the hospital.
Both doctors have worked on insanity cases in the past. The psychiatrist is Susan Fiester, who testified for the defense in the Lorena Bobbit trial.
Investigators, meanwhile, continue to search for evidence that Weston's attack was premeditated.
CNN has obtained a FBI inventory from the search of Weston's Illinois home one day after the shootings.
It lists various file cabinets filled with letters regarding the U.S. government, including the CIA and the military. At least nine boxes of ammunition for different weapons and two typewriters also were found.
"We're still struggling with a motive," one investigator said.