Rain complicated the grim work of recovering bodies from a passenger jet submerged in a swamp in central Africa, while the discovery of the flight data recorder increased chances experts will be able to determine what downed the Kenya Airways flight.

After rain on Monday, recovery teams were back at work Tuesday at the crash site, a mangrove swamp 12 miles from the commercial center of Douala, where the Nairobi-bound Kenya Airways Flight 507 took off moments before crashing early Saturday. All 114 people aboard were killed.

It took nearly two days to find the wreckage, most of it submerged in murky orange-brown water and concealed by a thick canopy of trees. The plane stopped emitting signals after an initial distress call, slowing the search.

Late Monday, the recovery teams found the plane's data recorder, one of its two black boxes, a development that could help investigators determine what happened on the flight. The second black box, which records conversation in the cockpit, has not yet been found.

At the site Tuesday, the search effort was divided into two teams — a military-led one in charge of gathering personal effects and another dedicated to human remains.

Thomas Sobakam, chief of meteorology for Douala airport, said the remains of 28 people had been found and some had been identified based on personal effects found with the remains.

"I can't tell you exactly how many have been identified so far — it's less than 28. Our goal right now is to get as many of the bodies out of the mud as possible. We have 28 out of 114 and until we get the rest, our priority won't change," he said.

Xavier Clopaire Noa, a Cameroonian firefighter helping in the search, said workers had tried to drain the swampy water from the crash site using pumps, but the effort failed. "We tried to empty it a few times but the water keeps coming back in," he said.

The stench of decomposing bodies and spilled fuel permeated the air Tuesday. A plastic wallet insert, containing a few dozen Chinese business cards and handwritten notes floated in the muck. Makeshift paths were cut through the area in an attempt to direct traffic and preserve the site.

Friends and relatives of those aboard were allowed at the site early Tuesday, but rescuers later barred them from the area in an effort to preserve evidence.

Lydienne Eyoum, a lawyer, had two friends on the plane, both employees at her Cameroon-based law firm. She walked through the brush from the scene Tuesday, leaning on the arms of a rescue worker, weeping.

"I couldn't believe it," she said. "But I wanted to see it to understand, because there are so many questions and no answers."

Kenyan President Mwai Kibaki declared a national day of mourning and, in a televised address, offered condolences to friends and relatives of the dead.

"I wish you the strength and courage to overcome the tragic loss of your loved ones," he said.

Flight 507, a 6-month-old Boeing 737-800, sent a distress signal shortly after takeoff Saturday from Douala. Its departure had been delayed an hour by storms. It lost contact 11-13 minutes later.

The early investigation focused on whether the plane lost power in both engines and did not have enough altitude to glide back to the airport.

The wreckage was found along the plane's expected flight path. Procedures for losing all power in an aircraft call for the pilot to try to return to the airport along the same path. The jetliner crashed nose-first, consistent with a plane stalling as a pilot desperately tries to coax it along the glide path.

Among the 105 passengers was Nairobi-based Associated Press correspondent Anthony Mitchell, 39, who had been on assignment in the region. A U.N. refugee agency official, Akouvi Enyonam Kumodzi-Agbeviade, who had been on a mission in the Central African Republic, also was on board, according to U.N. High Commissioner for Refugees spokesman Ron Redmond in Geneva. Nine crew members also were on board.

Officials said it was too early to tell what caused the plane to go down so soon after takeoff. Crash investigators focused on the stormy weather as a contributor, including whether the plane lost power in both engines as a result of the storm and if the aircraft's radar failed due to the power outage.

While air travel in Africa is notoriously perilous, Kenya Airways is considered one of Africa's safest airlines. The last crash of an international Kenya Airways flight was on Jan. 30, 2000, when Flight 431 was taking off from Abidjan, Ivory Coast, on its way to Nairobi. Investigators blamed a faulty alarm and pilot error for that crash, which killed 169 people.

Get complete coverage in FOXNews.com's Africa Center.