The sister of James DiMaggio, the man who kidnapped San Diego teen Hannah Anderson and killed her family, claims FBI agents used excessive and unjustified force in killing her brother after his actions spurred a large manhunt across six states.

Attorney C. Keith Greer filed an over $20 million wrongful death claim against the FBI Thursday on behalf of Lora DiMaggio Robinson, alleging that there was no “viable justification” for DiMaggio’s shooting death.

In the document, Greer said deadly force was not warranted given DiMaggio’s “history of nonviolence” and the number of agents there could have restrained him. According to the claim, DiMaggio had fired his gun in the air as a call for help, but he had not threatened Anderson with deadly force or “imminent harm.”

"There were just too many questions out there," Greer told NBC 7 Thursday. "Robinson knows that her brother was a very kind man, certainly not one to shoot at an FBI agent. So from the beginning she just felt like there was something that was being misportrayed about her brother."

As they investigated the case for a year, Greer said the evidence produced more questions than answers. According to the claim, FBI agent's deadly force was "unduly, excessive, prejudicial and unjustified." Read the full claim below.

The court document also alleges that FBI and Department of Justice employees conspired to keep secret information and evidence that could prove agents were responsible for DiMaggio’s death.

However, in May 2014, federal and state prosecutors said FBI agents acted reasonably when they shot and killed DiMaggio in the Idaho wilderness and the agents who killed him would not face charges.

Federal and state prosecutors say FBI agents acted reasonably when they shot and killed kidnapping and murder suspect James DiMaggio in the Idaho wilderness last summer after he kidnapped San Diego teen Hannah Anderson. NBC 7’s Bridget Naso speaks with Hannah’s grandmother who also believes the shooting was justified.

NBC 7 has reached out to the FBI for comment, but we have not heard back. The Anderson family said they have no comment at this time.

Greer said the first person they want to testify is Anderson to give her account of the harrowing events that began on Aug. 4, 2013.

That day, DiMaggio, a family friend, killed Anderson's mother and younger brother, Christina and Ethan Anderson, and set fire to his own home in Boulevard, Calif., before fleeing to Idaho with Anderson, prosecutors say.

The charred bodies of Christina and Ethan were discovered by sheriff’s deputies and fire officials at DiMaggio’s burned-out property.

According to search warrants, investigators believe DiMaggio “tortured and killed” Christina and Ethan on Aug. 4 before kidnapping her 16-year-old daughter. San Diego County Medical Examiner’s reports say Christina was bludgeoned to death, bound and gagged, while Ethan's remains were so badly charred they were practically beyond recognition.

Once Anderson’s disappearance was discovered, officials issued an Amber Alert that covered six states. The pair ended up in the rugged Idaho backcountry near Cascade and Morehead Lake, where they were spotted by a group of horseback riders on Aug. 7.

The group wasn’t aware of the Amber Alert when they crossed paths with the pair, but they learned about it immediately after their trip. The riders reported their sighting to authorities, leading more than 200 federal, state and local law enforcement officials to the rural community in Idaho in search of Anderson and DiMaggio.

According to Robinson's claim, the pair was ultimately spotted by a U.S. Marshalls plane, and an FBI hostage rescue team was dropped in close to their location on Aug. 10. At that point, Anderson and DiMaggio were trying to find rescue by building a fire for smoke signals, according to her interview on NBC's "Today" show.

When it proved unsuccessful, Anderson suggested DiMaggio fire a round from his gun, which was about 20 feet away, to draw attention, Greer said. As soon as the gun went off, DiMaggio was shot six times by FBI agents.

"Why don't they say, 'Stop, freeze, put your hands in the air, you're under arrest' at that point in time?" Greer said. "Why do they let him wait to go to... till he picks up the gun and, once he has the gun in his hands, shoot him? It didn't seem like he was treated fairly, regardless of what the allegations are."

Greer said Anderson holds the key to proving or disproving their claim, since she has a firsthand account. The attorney also hopes the FBI team was wearing body cameras so they could obtain recorded footage of the incident.

"What is definitely wrong is that he didn't have the opportunity to have his day in court," said Greer of DiMaggio.

If Anderson gives her deposition, it would not be the first time she has shared her story.

Days after her rescue, Anderson fielded questions about her kidnapping on social media and made brief appearances at local fundraisers in Lakeside.

A new book by Chelsea Hoffman identifies inconsistencies in Hannah Anderson’s very public discussions of how the crimes occurred. NBC 7’s Dave Summers reports.

In late August, Hannah spoke out about her ordeal in the media for the first time in a tearful interview on NBC's "Today" show. Later that month, Hannah and her family held an emotional memorial service for Christina and Ethan in San Diego's Santee community.

A short time after the service, the teen was reportedly back on social media, answering questions online about her life and the kidnapping.

In October 2013, Hannah appeared on “Today” once more to discuss her harrowing ordeal at the hands of DiMaggio. The teen said DiMaggio “drugged” her and said she passed out in his car during the road trip from San Diego to Idaho.

In March, Hannah’s grandmother told the media that her granddaughter continues to undergo therapy and will likely do so for “quite some time.”