A 63-year-old man is suspected of being involved in the explosion in Nashville on Friday.
Police sources tell CNN that it could be a suicide.
Song should have been played
On Sunday, some of the police officers who were first on the scene told about the incident.
The camper had issued a warning message and then they heard the song "Downtown" by Petula Clark played.
- I was standing by my car and heard my colleague say that the music started playing.
I went closer and felt "oh god", says police Amanda Topping to WTVF.
Residents evacuated
Authorities have now closed a Murfreesboro road, east of Nashville, when a truck was heard making "similar noises".
In addition, residents have been evacuated, writes the news agency AP.
The text is updated