"Formal suspicions are currently being brought against them," said Nerijus Puskorius of the Organized Crime and Corruption Investigation Division at Vilnius Regional Prosecutor's Office.
Officials said earlier they had detained Andrius Lobovas and Antanas Kandrotas in the investigation but did not name the third suspect.
Lobovas became known to the public during the so-called Garliava events. Kandrotas is known by the nickname Celofanas (Cellophane).
Prosecutors promised to provide more detailed information later.
Vilnius prosecutors say the riot investigation includes narcotic substances found in the possession of some of the rioters and suspicions of illegal collection of information on private life. The latter suspicion was added after offers appeared on social media sites to disclose, for a payment, the personal data of officers involved in suppressing the riot.
"There is one investigation and three articles," Romualdas Betingis of Vilnius Regional Prosecutor's Office, the prosecutor in charge of the investigation, told BNS.
Some 5,000 people gathered outside the parliament building on August 10 to protest against the government's plans to impose restrictions for people without coronavirus immunity or negative test results.
The rally turned violent in the evening, with some protested blocking exits from the parliament and throwing bottles and flares at police officers. The police used teargas against protesters.
Officials said earlier that a total of 38 people had been detained in the pre-trial investigation.