Judge unexpectedly resumes inquiry into the blast after it was paralysed for more than a year by political resistance and legal complaints.
It was not immediately clear what they had been charged with, but one judicial source said Judge Bitar had found Mr Oweidat had not acted responsibly with regards to the ammonium nitrate.
The group has campaigned against Judge Bitar as he sought to question its allies and it also accused Washington of meddling in the probe. Hezbollah leader Sayyed Hassan Nasrallah repeatedly called for him to be replaced in 2021. The court has been awaiting the appointment of new judges to resume its work, a step authorities have not taken.
Mr Diab, an academic, became prime minister in January 2020 and resigned less than a week after the blast.