(NEXSTAR) – A year after supporters of former President Donald Trump stormed the U.S. Capitol building on Jan. 6, 2021, resulting in the deadliest domestic attack on Congress in the nation’s history, the Justice Department and FBI are still working to charge and process those involved.

Some notorious suspects, such as the masked, hooded figure who left pipe bombs outside the offices of the Republican and Democratic national committees in Washington D.C. 17 hours before the insurrection, have yet to be identified.

As of this week, the FBI says it has interviewed more than 900 people, worked over 400 leads and amassed nearly 40,000 video files in an attempt to identify the would-be bomber.

The shrouded suspect is just one of hundreds who authorities are still searching for – the FBI hopes to identify 250 people seen on video assaulting police and another 100 for crimes tied to the riot.

As for those who have been identified, the Associated Press reports that more than 700 people have been charged with federal crimes stemming from the Jan. 6 attack. Exact numbers are difficult because arrests are still being made regularly across the country.

“This investigation takes time because it is a lot of lot of work, a lot of painstaking work that they look at the video kind of frame by frame,” said Steven D’Antuono, the assistant director in charge of the FBI’s field office in Washington.

In one case, police body camera footage captures a man using a cane with electric prods on the end jabbing at officers and shocking them as they fight to hold back the riotous crowd trying to break through a barricaded line of officers at one of the doors of the Capitol. The crackling sound of the electricity can be heard as he prods his cane into one of the officers. The man, known only as “AFO114” — using shorthand for “assaulting a federal officer” — is still being sought.

“The assaults against the police officers are extremely serious,” D’Antuono said. More than 100 police officers were attacked by rioters on Jan. 6, some attacked by multiple people and some attacked multiple times,” he said.

In another video, a man is seen repeatedly bashing a police officer over the head with a 6-foot (1.8-meter) metal pole as he tries to push his way into the Capitol. And a third shows a man spraying some kind of chemical from a can into the faces of other officers.

“There is still a lot of work to be done on this,” D’Antuono said. “There were a lot of people up there at the Capitol, a lot of people that either committed violence up there did other unlawful actions up there.”

The Justice Department has faced stiff criticism for failing to level serious charges of sedition or treason at the rioters, with most of the roughly 160 who have pleaded guilty receiving sentences of six months or less. Only a handful have received more than two years in jail, but hundreds of cases are still working their way through the court system.

The Associated Press contributed to this report.