HOUSTON — It seemed like a tragic mistake.

A young father, held for ransom, was shot and killed in January 2018 — not by his kidnappers, but by an FBI agent trying to save him. The agent had fired into a dark room where the hostage had been tied up alone.

But a dramatic twist came in October: The Houston police chief, whose department investigated the incident, announced that the FBI agent's story didn't add up.

"Our investigative findings do not support the description of how the shooting occurred by the shooting agent," Chief Art Acevedo told reporters.

Two law enforcement sources familiar with the matter told NBC News that the FBI and federal prosecutors are examining whether the agent gave a false account, whether he acted negligently, and whether the pre-dawn raid by heavily armed FBI personnel was properly planned and executed.

But relatives of the victim, Ulises Valladares, say they've been told nothing. They say they don't know the agent's name or whether he's still on duty. They have filed a wrongful death lawsuit, which is pending.

Ulises Valladares with his son, Junior. Photo blurred by source. Courtesy of the Valladares Family

The Houston case became the latest in a series of incidents in which an FBI agent's actions with a gun have come into question, according to a review of public records by NBC News. And it underscored what critics say is a troubling culture of secrecy at the nation's main federal law enforcement agency.

New FBI data obtained exclusively by NBC News shows the bureau found fault with the actions of agents five times in 228 shooting incidents from 2011 to the present. Eighty-one were intentional shootings involving people or objects, 34 were intentional shootings of animals, and 113 were accidental discharges.

FBI officials refused to discuss any of the internal investigations into each shooting or answer any questions about whether agents were disciplined. They declined to comment on the Houston case.

By determining that the actions of the five agents were unjustified, FBI officials said, the bureau was not saying that an entire shooting was unjustified. None of the five questionable shooting actions by agents led to a death, officials said. It is possible, they said, for multiple agents to have shot to death a suspect in a manner that followed all the rules, only to have one agent fire a shot that was deemed improper.

"Each round is evaluated," one FBI official said.

The home where Valladares was held hostage and killed in Houston, Texas. NBC News

Aside from the Houston incident, other recent FBI gunfire has come under scrutiny:

In August, an FBI agent was acquitted of federal criminal charges that he lied about firing his weapon in a 2016 standoff with right-wing extremists in Oregon. The FBI declined to comment on any disciplinary investigation.

In June, an FBI agent — off-duty but armed with a handgun — accidentally shot someone in a Denver nightclub after he did a backflip that dislodged his weapon. He pleaded guilty to third degree assault and was sentenced to two years probation. The FBI would not discuss his status at the bureau.

In 2016, an FBI agent shot a 31-year-old man during a military-style raid to serve a warrant on a different person. The FBI says the man was armed; his family, which has filed a wrongful death lawsuit, disputes that and adds that he was blind in one eye and disabled. The FBI declined to comment on the case.

In 2015, the FBI terminated an agent who fired his weapon from a second-story apartment in Queens, shooting an unarmed man as he tried to burglarize the agent's car on the street below.

FBI officials would not comment on any of those cases.

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"I think the public should be concerned where we have government agents using force without appropriate accountability, and that accountability requires transparency," said Michael German, a former FBI agent who is now a fellow with the Brennan Center for Justice's Liberty and National Security Program. "Unfortunately, the FBI's process is not only not independent — it's the FBI investigating itself — but it's not very transparent."

FBI officials disagree, describing their investigative process as meticulous and fair. But the bureau has declined to follow the lead of many of America's largest police departments, which publish annual reports detailing each use-of-force incident. New York City police, for example, report how often a firearm was discharged, who was hit, and under what circumstances. Los Angeles and Washington, D.C., do the same. Houston publishes statistics about officer-involved shootings.

The bureau's inspection division produces an investigative report for each agent-involved shooting, but the only time the bureau made some of those public in recent years is after the New York Times sued under the Freedom of Information Act, resulting in a story published in 2013.

The redacted records the Times obtained showed that from 1993 to early 2011, FBI agents fatally shot about 70 people and wounded about 80 others. Each one of those shootings was deemed justified.

The bureau's public affairs office declined a request by NBC News for copies of investigative reports for shootings that occurred subsequent to those reflected in the Times data. An FBI spokeswoman instructed a reporter to file a Freedom of Information Act request — a response to which can take years, due to an enormous backlog. NBC News filed a request, but the FBI turned down an appeal for expedited processing. NBC News argued that the public had an urgent need for more information about FBI shootings, but the bureau disagreed.

The FBI recently launched a campaign to encourage police departments to publicly disclose information on their use of force, as part of a national database the bureau is seeking to build. A video on the FBI website featured local officials promoting the program.

"Any time that information is not readily available, that breeds skepticism. Skepticism leads to distrust," Sheriff Bob Gualtieri of Pinellas County, Florida, says on the video, as stirring music plays in the background.

"What that data really does is allow us to be transparent in the force that we use in our everyday situations," Gina Hawkins, chief of police in Fayetteville, N.C., says on the video. "This transparency is not all the time easy. It may involve us owning up to we could have made a better decision. … To be transparent is what builds the trust of the community that we work for."

FBI officials said the bureau itself would also submit information to the database, but that no data has yet been made public.

How the FBI investigates itself

Bureau officials, declining to be named for the record, told NBC News that the evidence gathered in shooting investigations includes interviews with the agents involved. The agents are required to answer questions — in a formal interview with a lawyer representing them.

The evidence is often shared with local prosecutors, and is then turned over for examination by the FBI's Shooting Incident Review Group, which meets quarterly and votes on whether the agents' actions in each shooting incident were justified.

Frank Figliuzzi, an NBC News law enforcement analyst, spent 25 years at the FBI, including a stint as chief inspector, leading investigations of agent-involved shootings. He was a nonvoting member of the incident review group.

Ulises Valladares of Conroe, Texas. via Facebook

Even when the use of lethal force has been deemed valid, he said, "these reviews frequently identify tactics, methods or conduct that can be improved upon."

At times, he said, an agent's use of deadly force may have clearly been within FBI policy, but the reviewers find that he or she should have employed different tactics or approaches that could have precluded the deadly confrontation.

In those cases, a review of practices, training, counseling or even discipline is recommended — but that is not reflected in the FBI data on whether shootings are deemed justified, he said.

"This accounts for a seemingly low percentage of FBI shootings being found to be 'out of policy,'" he added. In many cases, "a comprehensive review may have found that best practices were not followed, despite a 'good shoot'."

Justice delayed?

In the Houston case, Acevedo told reporters the agent said he stuck his M4 rifle through the window of the house where Valladares was bound on the couch. The FBI was storming the residence to free the hostage, who had been seized by men who said his brother owed them money.

Somebody inside grabbed the rifle, the agent told police, leading him to fear that he would lose control of it. He fired two shots, striking Valladares, the only person in the room.

At his news conference in October, Acevedo said he no longer believed that story. The chief didn't say what he thinks really happened, so as not to disrupt the pending federal investigation into the matter. He declined an NBC News request for an interview, and federal prosecutors declined to comment.

Acevedo told reporters in October that he didn't understand why the federal investigation was taking so long, given that the Houston Police Department turned over its findings in April.

"I've always say, justice delayed is justice denied," he said. "For everyone involved. For the FBI agent — and his family — I would hate to have something like this hanging over me. For the family of Mr. Valladares, who want to know exactly what happened."

From left, Jimmy Tony Sanchez, Nicholas Chase Cunningham and Sophia Perez Heath. Conroe Police Department

Valladares' 13-year-old-son, whom NBC News is not naming, does want to know. His mother died of cancer the year before. He was there the day the armed men took his father. They tied him up, as well, and he wriggled free to call for help.

"He's kind of at a loss," said the woman now raising him, his older half-sister Brooke Pearce. "His heart's definitely hurting."

Pearce had to withdraw from nursing school to raise her younger brother along with her own child. More than a year after the shooting, she is still waiting to learn how the FBI agents who came to rescue her brother ended up killing him.

"I don't feel like anything was handled appropriately. You're not really reassured that the person was reprimanded or if they were given any additional training or even if they're still out there with a gun running at people's homes in situations like this."