Serbian prosecutors on Tuesday requested the arrest of 13 suspects linked to the fatal collapse of a train station roof in November that has triggered waves of anti-government demonstrations.
The disaster at the newly renovated station in the northern city of Novi Sad became a symbol of entrenched corruption.
Protesters' demands for a transparent inquiry have escalated into calls for early elections.
Three separate probes have been launched, including one led by the European Union that alleges corruption and possible misuse of public funds.
Here are key details of the ongoing investigations.
- The investigations -
Novi Sad prosecutors launched a criminal investigation and in December charged 13 people, including former construction minister Goran Vesic.
They filed an indictment against the suspects but judges returned it in April, requesting more information.
The accused were either released or placed under house arrest.
On Tuesday, however, all 13 were re-indicted on charges of "serious crimes against public safety", and the prosecutor asked the court to arrest them again.
The court will now decide whether to proceed with the case.
A separate financial probe -- led by Serbia's corruption and organised crime prosecutor -- is underway into the funding of the railway reconstruction project.
Thirteen people were arrested in this investigation, including Tomislav Momirovic, who was the construction minister when the renovation began.
All have since been released and no indictments have been filed in this case yet.
In March, the European Public Prosecutor's Office (EPPO) launched its own investigation, still ongoing, into the possible misuse of EU funds for the station rebuild.
The suspects
More than 20 people are named as suspects in the probes.
Vesic appears in both Serbian investigations, along with his junior minister, Anita Dimoski.
The criminal inquiry also targets construction designers, contractors, supervisors and inspectors, including two engineers from French firm Egis.
Along with Momirovic, suspects in the financial investigation include officials from state companies and several private firms linked to the reconstruction project.
The EPPO has not released any details of suspects.
The charges
Those indicted in the criminal investigation for endangering public safety face a potential prison sentence of two to 12 years.
The financial probe centres around suspected corruption linked to the project, which investigators said cost Serbia's budget over $115 million.
They also allege that Chinese consortium CRIC&CCCC -- which is behind the high-speed railway that runs through Novi Sad's station -- secured at least $18.7 million in unlawful gains.
European Chief Prosecutor Laura Kovesi told Serbia's national broadcaster that the EPPO's case centres around European Investment Bank loans for the railway and station works.
Government view
President Aleksandar Vucic has condemned the arrest of former ministers as "scandalous" and repeatedly accused anti-corruption protesters of being part of a foreign coup.
Vucic, who is facing the biggest challenge to his party's 13 years in power, has promised justice over the tragedy but has also claimed: "The prosecution is making a mockery of us all."
Backed by pro-government media, the right-wing head of state has used his platform to undermine prosecution efforts targeting his administration.
Protesters' view
Ten months on from the roof collapse, which killed 16 people, protesters have continued regularly to turn out in large numbers, voicing frustration over the glacial pace of investigations.
"No-one has been held accountable, no-one dismissed... Nothing," Lazar, a final-year university student, told AFP at a Belgrade rally earlier this month.
A bloodied handprint has become the enduring symbol of rallies alongside banners reading "Crime, not tragedy" and "No justice for the people, no peace for those in power".