was started/had been started

[kohyoongliat]

Since this incident, Mr Koh has closed all the windows in the living room before going to bed. He believes that the fire had been/ was started by a vandal who set fire to his curtain through the open windows.

Should I use 'had been' or 'was'?

Thanks in advance.

[Tdol]

'Was' sounds more natural to me.

[kohyoongliat]

Thanks, Tdol.