The FBI is investigating the death of an inmate at the Fulton County Jail and whether jailers beat the man so badly he died from his injuries, according to two people familiar with the investigation.

Fulton Sheriff Myron Freeman's office, which oversees the jail, confirmed the investigation Thursday but would not give details.

But a jail expert who is monitoring the jail under a court order confirmed that the federal investigators are looking into the March death of inmate Richard Glasco. "They want more information. They want to know everything about it," Calvin Lightfoot said. "I think the [inmate's] family has brought this to the attention of the federal prosecutor."

FBI spokesman Stephen Emmett and Patrick Crosby, who speaks for U.S. Attorney David Nahmias, would not confirm nor deny any on-going case, which is the practice of both offices when asked about pending investigations.

But two people familiar with the FBI's questions and the information investigators have requested, said agents have asked for a number of records on jail staffing and the movement of staff inside the jail on the day Glasco died.

The two people familiar with the investigation, who asked to not be named because the inquiry is ongoing, said it is focusing on whether guards inside the Fulton jail beat Glasco.

The two also said least six inmates were removed from the jail following the death and locked up somewhere else because they might have witnessed circumstances surrounding Glasco's death on March 19. Mike Alsip, an investigator with the Fulton County Medical Examiner's Office, said a cause of death for Glasco, 42, has not been determined, but it's being treated as a "sudden, unexpected death."

Lightfoot's most recent report on the jail's progress toward meeting the federal court's requirements included Glasco's death on a list of three in-jail deaths from January to March. Lightfoot wrote that Glasco's death "is thought to be heart failure."

The Atlanta police arrested Glasco Feb. 15 on numerous charges such as obstruction of a law enforcement officer, making terroristic threats and disorderly conduct. He was being held in jail on an $80,000 bond, awaiting a court date.

According to Lightfoot's report, on the day he died, Glasco was taken to a court appearance and became "disruptive" on the trip back to the jail. "Glasco pounded with his fists on the cell door/window and he continued to kick on the door/window and walls as he shouted at staff," Lightfoot wrote in the report. He said Glasco was later found unconscious in his cell by jailers.

Lightfoot said in an interview Thursday, that the information in his report was based on what the jail staff told him and his auditor on the scene and he had not confirmed it through any other sources.

"There's no way for us to know what's accurate and what's not accurate," Lightfoot said. "[The jail has] control over us with the kind of information that they give us." Lightfoot said he has not been contacted by the FBI.

Freeman said in an e-mailed statement his staff will "cooperate fully with investigators." The statement did not include specifics about what federal investigators were seeking.

"I look forward to learning the outcome of this investigation," Freeman said in the statement. "We welcome their assistance. From the highest level employee to the rookie new hire, we will provide investigators with any information and help they require."