Police confirmed that both Jackass star Dunn and Hartwell died as a result of injuries they suffered in the crash, which was timed at 2.38am Monday morning local time, TMZ reports.
The authorities had previously confirmed that Dunn had been driving the Porsche 911 GT3 at the time of the accident.
Hartwell has been identified as one of the two friends who Dunn had been photographed drinking with at a bar earlier in the evening.
Sources told the website that Dunn had planned to drop Hartwell home on the morning of the accident before moving on to meet with another friend.
Hartwell played the minor role of 'Agro Trailer Park Guy' in the Bam Margera-directed 2009 movie Minghags and was also a car stunt driver on the project.
Margera this morning hit out at film critic Roger Ebert for his online comment that "friends don't let jackasses drink and drive".
> Ryan Dunn death mourned by 'Jackass' co-stars
Watch a video of Jackass star Ryan Dunn performing a stunt with a bottle of tequila below: