One inmate was killed and another was wounded in separate stabbings over the weekend at the D.C. jail, just days after a third detainee was slain in a similar attack, corrections officials and prisoner advocates said yesterday.

The killings were the first at the Southeast Washington facility in nearly five years, according to corrections officials. Police said the three stabbings do not appear to be related. Two sources familiar with the investigation said that police have possible suspects in each of the incidents, but no one has been charged.

The inmate-on-inmate attacks took place over a 70-hour period in different cellblocks. Officials with the D.C. Department of Corrections said they put the jail on an indefinite lockdown after the latest incident Saturday, restricting movements and activities of inmates, while D.C. police and the agency's internal affairs unit investigate.

The violence raised new concerns among jail watchdogs about whether the detention center can operate safely above a court-ordered population cap of 1,674 that was lifted in June after 17 years. Yesterday's inmate count was 2,369.

"There is reason to be concerned about security at this population level. There is something not right about the checks and balances," said Marie-Ann Sennett, executive director of the D.C. Prisoners Legal Services Project. She faulted the jail for not instituting a lockdown after Wednesday's fatal stabbing so that a full search for illegal weapons could have been done. Officials said they viewed it as an isolated incident.

The second fatal stabbing unfolded early Saturday evening. Mikal Gaither, 23, a pretrial detainee being held on charges of possession and intent to distribute cocaine, was stabbed in the neck on a walkway in the Northeast 3 cellblock, authorities said.

Gaither, who had been jailed since Dec. 3, was transported to Washington Hospital Center, where he died the next day. Police are investigating whether the stabbing stemmed from a dispute between Gaither and an inmate that began before they both were incarcerated.

On Friday, about 7:30 p.m., another inmate was slashed on the lip and elsewhere on his face in the Southeast 2 cellblock, authorities said. A corrections spokesman declined to identify the inmate, but a source said he is Autman Bradley, 43. He was treated at a hospital and transferred to the Central Treatment Facility, adjacent to the jail.

The episodes followed the stabbing Wednesday night of Givon Pendleton, 24, who was awaiting trial on charges of burglary and possession with intent to distribute cocaine. Authorities said Pendleton was stabbed as many as seven times in the head, abdomen and arm at 7:30 p.m. in the gym of the Southeast 1 cellbock.

Pendleton, who had gotten into a disagreement with another inmate over some milk, died later that night at Washington Hospital Center, officials said.

According to sources, investigators have found a shank or homemade knife-like weapon in a cell not far from where Gaither was stabbed. That instrument is being analyzed to determine whether it was the attack weapon, the sources said. But authorities have not located the weapon in the Pendleton killing, the sources said, and it was not clear last night if the one used in the stabbing Friday has been uncovered.

Before Wednesday night's fatal stabbing, the last time an inmate at the jail was killed by another inmate was in January 1998, when an 18-year-old man was thrown over a second-floor railing during a fight and died later that afternoon at D.C. General Hospital.

Earlier this year, prisoner advocates agreed not to oppose a court motion filed by the corrections department to have the population cap lifted. The agency argued that health and safety conditions at the jail had been addressed.

But Pamela A. Chase, chairwoman of the Fraternal Order of Police's unit at the Department of Corrections, said she opposed lifting the cap unless jail staff was sufficiently increased to handle the larger inmate pool. "Budget cuts times an increased inmate population makes for a deadly situation," Chase said.

She added that 564 corrections officers are assigned to the jail, but that 724 are needed to handle the higher number of inmates. Staff shortages, Chase said, have had dangerous consequences for corrections officers. She noted that there were about 15 assaults on officers between April and August of this year. In three of those assaults, one officer suffered a broken hand, another had to deal with temporary sight loss to one eye and a third had a broken nose and required 36 stitches to the mouth.

D.C. Council member Kathy Patterson (D-Ward 3), chairman of the Committee on the Judiciary, said that she and council member Sharon Ambrose (D-Ward 6) warned Mayor Anthony A. Williams (D) in November that they "were afraid the place was going to blow."