Rothschild Police Chief William Schremp said Monday the rollover crash remains under investigation.
Three EMTs were hurt when the ambulance driver lost control of the vehicle and it rolled over on Interstate 39 last Thursday evening.
The Mosinee EMTs were transporting 52-year-old David Nicewander to a Wausau hospital when the rollover happened.
Schremp says it was raining at the time and weather could have been a factor in the crash.
A Mosinee Fire Department employee on the job for 18 months was driving the ambulance.
The chief says the ambulance was inspected for possible mechanical problems, but the data has not been analyzed.