The two officers were only seven to 10 feet from where Philip E. Parker Jr. was killed by another prisoner.
An inmate on the bus who said he witnessed the killing said that the attacker sucked in his stomach to loosen his waist chain and used it to strangle the victim.
The inmate, who recounted the grisly scene in letters to relatives, said two people were involved in the killing, with one holding Parker down as the other slipped his loosened "belly chain" over the victim's head and pulled back.
"The killer sat down pulling the kid's head backwards over his seat, choking him," the inmate witness wrote. It seemed to the inmate that the attacker was trying to break Parker's neck.
"I could hear the killer tell him, 'It's okay. Just go to sleep now.'"
The letters were provided by a relative who said the inmate fears for his safety and does not want to be identified by name.
One of two officers in the caged area at the rear of the bus told union officials that he radioed two other officers in a separate compartment at the front of the bus, alerting them that something was wrong.
Following security procedures, the officers, who were armed with shotguns, didn't leave their area or stop the bus because of the danger that inmates could get hold of the weapons or the bus could be hijacked, a union official said. Instead, the driver sped ahead to the Maryland Correctional Adjustment Center - also known as Supermax.
When they arrived in Baltimore about 4 a.m. Feb. 2, Parker was found dead on the bus.
At the time of the incident, the bus, on its way from a Hagerstown prison, was on Interstate 70 in Baltimore County, near a Park & Ride stop just before Security Boulevard, according to the officer.
He told union officials he saw a shadow in the bus, shined his flashlight down the aisle and spotted an inmate, Kevin G. Johns Jr., 22, as he got up and moved around. He also reported seeing blood on Johns and that's when he called ahead to the driver that something was wrong.
Although inmates on buses are in three-piece restraints, with leg irons and handcuffs attached to a waist chain, they are able to stand and leave their seats, according to corrections officials.
"They were completely in the dark," said Ed Rothstein of the Maryland Association of Correctional and Security Employees. "How are they supposed to see if the lights are out?"
A second union official who requested anonymity obtained the detailed account from one of the officers about what happened as the bus headed for Supermax.
The union official said the officer insists that all 35 prisoners on the bus, including Johns, were in restraints and is mystified how Parker could have been strangled.
But a former inmate said in an interview he believed the waist chain could be used as a strangling device if it was attached too loosely.
A law enforcement source has told The Sun that Johns, a twice-convicted killer who strangled two other people, is a suspect in Parker's slaying.
Parker had been in court in Hagerstown testifying about Johns' mental instability the day before he was strangled on the bus.
Parker was summoned as a defense witness during a sentencing hearing for Johns in the strangling of a 16-year-old cellmate in January 2004.
The two men had known each other since they were in their teens and once lived together in a state-run facility for mentally and emotionally disturbed teenagers, according to court documents.
Parker testified that Johns needed psychiatric help. "I mean he's paranoid," he told the sentencing judge, according to a transcript. "He gots a really short temper, right. And he gets very easily irritated and agitated, right."
At the same hearing, Johns had vowed to kill again if he was not given psychiatric treatment. He wanted to be sent to the Patuxent Institution, a prison that treats inmates with serious mental illness, but that request was rejected.
The correctional officer who spoke to union officials told them that he and the other officers on board knew nothing about the threats in court, according to the union source.
The union official said four Supermax inmates who testified at Johns' sentencing hearing in Hagerstown would have been put in segregated cages away from each other if that had been known.
Rothstein noted problems with the bus. "We don't want these officers scapegoated for serious flaws in the design of the bus, including the problems of these lights being broken," Rothstein said.
State corrections officials have said little officially about Parker's killing. A corrections spokesman, Mark Vernarelli, said he could not comment on any details in the account The Sun received from the inmate witness or others about Parker's death.
"We can't comment specifically on any of the details that are out there, but we are very confident that this case will be presented to [prosecutors] very soon and we will be able to provide the public with significant answers to some of their questions regarding how this happened and what we may be able to do to prevent it from happening again," he said.
S. Ann Brobst, an assistant state's attorney in Baltimore County and chief of the Circuit Court division, said yesterday that Baltimore County prosecutors will be handling the case.
"Obviously, the evidence supports the theory that the crime occurred in Baltimore County," she said. The results of the investigation, Brobst said, will be presented to a grand jury within a month.
Sun staff writer Jennifer McMenamin contributed to this article.