The girl went missing in her neighbourhood on Wednesday and was found dead on Saturday afternoon.
The 27-year-old suspect had used a false name to secure a job at a neighbouring condominium project. In his application, he was identified as Chatree Seedee.
The man told police that he was drinking alcohol and got a sexual urge when he spotted the girl running around alone.
"We have checked recordings from security cameras in target areas since we received reports of the girl going missing," deputy Metropolitan Police Commissioner Maj-General Thitiraj Nongharnpitak said yesterday. "From these recordings, we found a man leading a girl towards an apartment block."
Police scoured the area until they smelled a foul odour coming from a sewerage pipe. When they opened its lid, they found the girl's body in a garbage bag. Her father cried when he saw the body.
The father said she went missing between 6pm and 8pm on Wednesday. His family initially believed she went to a market with her grandfather. But when the grandfather returned home alone, they realised she was missing.
Chatree told police that the girl was familiar with him, but she resisted his attempt to rape her and when she cried out for help, he strangled her.