Royal Thai Police's Commissioner General Office adviser Pol Lt Gen Jarumporn Suramanee said the evidence collected to arrest the men was from a camera of a citizen bystander showing three young men taking items from the bus. One was caught in the bus and burned to death.
The second man was identified as Adisorn Srichanpong, 29, and the third is a 15-year-old with his name being withheld due to his age. However, they denied torching the bus and said the dead man could not make it off the bus in time.
Authorities added that the dead man, 19 year-old Suradet Khampaengjai, was involved in the arson.
The bus was torched in front of Ramkhamhaeng Unviersity and the flames spread rapidly, locking Mr Suradet inside, causing his death.
The two detainees said they lived in Bangkapi district and were asked by a group of vocational school students to get on the bus and steal items from there.
Police said there are 23 related cases awaiting further investigation.