The priest has identified himself as Rev. Patrick Dowling of the Jefferson City Diocese. (FoxNews.com)
Here is the full comment he had posted at the National Catholic Register's original story on the incident (text taken from cnn.com since the comment has since been deleted) (broken into paragraphs by me):
Why he wasn't recognized:
I had Mass in Ewing MO as the regular priest was sick.
His arrival at the scene:
As I was returning, I arrived at the scene. The authorities were redirecting traffic. I waited till it was possible to drive up closer. I parked behind a large vehicle about 150 yards from the scene. I asked the Sheriff’s permission and approached the scene of the accident.
What he did:
I absolved and anointed Katie, and, at her request, prayed that her leg would not hurt. Then I stepped aside to where some rescue personnel and the pilot were waiting, and prayed the rosary silently.
How he left:
I left when the helicopter was about to take off, and before I got to my car it was on its way to Quincy. [...] I gave my name to one of the authorities, perhaps to the sergeant of Highway Patrol, explaining that I was returning having celebrated Mass at Ewing. It was the sergeant who, at the Sheriff’s request, gave me Katie’s name as I was leaving, so I could visit her in hospital—I assumed she would be taken to Columbia.
The comment has since been removed at his request, but he discussed the incident with the National Catholic Register for another story.
About the claim that the preist said "Lentz would now be freed", Dowling says that he did not say that:
“I didn't say another word,” he said. “I did not say anything like the machinery would begin to work or they would succeed in getting her out of the car.” “That did not come from my lips, though two people heard it.”