Investigators tried to determine Tuesday why an Indonesian jetliner crashed into a neighborhood seconds after takeoff, killing at least 149 people. Weeping families looked for loved ones at a morgue, and authorities readied a mass grave for the unidentified.

Remains not identified by early Wednesday will be buried next to another mass grave for victims of a 1997 Garuda Indonesia plane crash that killed more than 200, said Dr. Suprato, the assistant director of the Adam Malik Hospital in Medan (search), who was helping with recovery efforts.

Those killed when the Mandala Airlines (search) Boeing 737-200 crashed Monday in Indonesia's third-largest city included 47 people on the ground. Fifteen people aboard the flight survived, including an 18-month-old boy who was sitting on his mother's lap.

Transport Minister Hatta Rajasa (search) said it would be several weeks before the cause of Monday's crash was known, but investigators were looking at what happened during takeoff. Survivors said the plane shook violently right after takeoff and veered left before crashing.

Both flight data recorders have been found, officials said, and will be sent abroad for analysis.

Indonesia officials ruled out terrorism in the crash — a constant fear in the world's most populous Muslim nation, which is home to the Al Qaeda-linked Jemaah Islamiyah terrorist group.

Soon after dawn Tuesday, investigators arrived at the massive crash site yards from the runway. The area was taped off, but police were unable to keep people from the scene. Hundreds milled about, covering their noses with handkerchiefs as they pointed at the plane's tail, a piece of the wing and twisted knots of blackened metal.

Indonesian Air Force Lt. Andri, who goes by a single name, said searchers recovered body parts from the debris.

Setio Raharjo, head of the National Transportation Safety Board and the lead investigator, said the curious onlookers could be hampering efforts to get to the bottom of the crash.

"No cockpit or flight instruments have been discovered," he told El-Shinta radio, calling on local authorities and residents to return anything taken from the scene.

Survivors said the jetliner started shaking violently when it reached an altitude of about 100 yards. It then veered sharply to the left and crashed in a ball of fire onto one of the city's busiest roads, skidding 200 yards before grinding to a halt.

Outside the Adam Malik Hospital morgue, about 90 blackened bodies were laid out on yellow sheets under a tent. Sobbing relatives went from corpse to corpse in desperate searches for parents, sons and daughters. Others enlisted the help of people who claimed to have paranormal powers.

By late Tuesday, 64 corpses had yet to be claimed, the hospital said.

"I found my son-in-law because I remembered the trousers he was wearing," said Asiyah, 50. "But I cannot find my daughter. I will stay here until I do."

President Susilo Bambang Yudhoyono toured the crash site on Sumatra island after attending the funeral of the north Sumatra governor, one of the victims. Indonesia's red-and-white flags were at half-staff across the city.

Survivors recounted tales of horror.

Fritina, 32, was clutching her 18-month-old son when the plane lost control. The toddler survived, but her oldest son did not.

"She's not talking much," said her father, Haji Muhammad Ersani, 62, after visiting the pair in hospital. "She's in shock. She only remembers that when the plane went down and split apart, she immediately got out and watched as her eldest son was on fire."

Another passenger, Fredi Ismail, managed to crawl out of a hole in the fiery wreck only to realize his 47-year-old wife Helda Suriani was still trapped inside.

"I heard her screaming. She couldn't get her safety belt off," Ismail, 52, told Metro TV. "So I went back in, hugged her and pulled her out to the grass ... Then a man came in a van and drove us to the hospital. I want to thank him."