The engineer investigating the collapse of a walkway in Jakarta that injured 72 students says he's been blocked from inspecting critical parts of the failed structure.

Key points: Engineer investigating collapse of walkway says police blocked him from site

Engineer investigating collapse of walkway says police blocked him from site Worst-injured remain in ward at Indonesian military hospital

Worst-injured remain in ward at Indonesian military hospital ABC ordered to stop interviewing injured and to leave hospital

"I don't have access to go in," Steffie Tumilar told the ABC.

"The cooperation is not so smooth."

Steffie Tumilar is a veteran construction engineer appointed by the city Government to work out why the mezzanine walkway at the Jakarta Stock Exchange building crashed to the ground.

He's been unable to do his job.

"I've said to the Government if there's no cooperation I don't want to investigate more," he said.

Steffie Tumilar said police blocked him from going in to the site. ( ABC News: Phil Hemingway )

He's prepared a limited report based on CCTV footage of the collapse and a quick inspection of the site.

He has not been able to look at the crucial components that failed: the bolts, beams and clamps that suspended the walkway three metres above the building's ground floor.

The stock exchange building is 20 years old and it's likely the collapse was caused by a worn-out or overloaded clamp or fixture.

But investigators can't be certain because they haven't looked at the parts.

Mr Tumilar said police blocked him from going in.

Police said access was now out of their hands because they handed the site back to building management.

It's an important investigation. The walkway's failure suggests serious problems not only with its design — it should have been strong enough to withstand the failure of a single connection — but it also indicates broader problems with maintenance and inspection in Jakarta.

And if it could happen at a top-tier building that houses companies like the World Bank and the Stock Exchange, it could happen anywhere.

Sorry, this video has expired WARNING: Distressing content - CCTV shows the moment Jakarta stock exchange floor collapses

Injured remain in hospital

Seventy-two people were hospitalised after the accident — most of them young accountancy students from a university on the island of Sumatra.

Desva Hara, 21, fractured her bones and remains in hospital. ( ABC News: Phil Hemingway )

The worst-injured remain in a ward at an Indonesian military hospital: The hospital granted the ABC permission to speak to 21-year-old Desva Hara, who has fractured bones.

"My hand was trapped under my friend — and when I tried to stand up my hand couldn't move."

Deka, 21, says she will have to learn how to walk after her bone recovers. ( ABC News: Phil Hemingway )

Another 21-year-old student from Bina Darma University, Deka, is recovering after her pelvic bones separated from the force of the impact.

She has long pins drilled into the bones of her leg to hold them together.

"My leg is still being treated, the doctor told me to stay for another two weeks, so the bone can go back normal, then I have to learn how to walk, then I can go home," she said.

Deka has long pins drilled into the bones of her leg to hold them together. ( ABC News: Phil Hemingway )

ABC ordered to leave hospital

Sorry, this video has expired ABC ordered to leave Indonesian military hospital

As we're interviewing the military surgeon who operated on Deka, a man in civilian clothes enters the ward and demands to see our IDs.

We handed them over, and he asked us to leave.

It's only then that we asked him to identify himself … and it became clear he was not with the military or the hospital.

"You should finish," he told us.

We ask him his name and he replied, "Agus Pratikno".

He said he was from building management.

Incredibly, Mr Pratikno works for the company that owns the Jakarta Stock Exchange building — one of the companies under investigation over the collapse.

But it appears he holds some power in the hospital — and we're escorted out of the building.

Just like construction engineer Steffie Tumilar our access has been denied.