On Feb. 1, the woman allegedly sent a threatening email to Delph, a Republican from Carmel.
The e-mail allegedly took the senator to task for his support of a contentious immigration bill, which passed through the Indiana Senate this week.
The e-mail allegedly said the man suspected of shooting U.S. Rep. Gabrielle Giffords should have targeted someone like Delph, the Associated Press reported.
The Indiana State Police investigated the case but made no arrests, police said.
The case was then sent to the St. Joseph County prosecutor’s office on Feb. 10 for review.
Prosecutor Michael Dvorak reviewed the case and sent it to the U.S. attorney’s office, given the nature of the threats, he said. But the prosecutor did not elaborate.
"I don't want to go into it at this time because I don't want to say anything that might jeopardize the ongoing nature of this matter," Dvorak said.
Dvorak said the U.S. attorney's office is still reviewing the case.
He said there have been "no decisions about whether or not the evidence we have is sufficient, or whether the alleged statements necessarily constitute a state crime or federal crime."
Officials did not release the woman’s age or where she lives in St. Joseph County. State police said she was in her late teens or early 20s.
Delph’s immigration proposal would require police to ask for citizenship or immigration status if they have reasonable suspicion that a person is in the country illegally.
It passed the Senate last week and is headed to the state House of Representatives for consideration.
The e-mail was critical of the bill and racial profiling, the AP reported, and was addressed to "Senator Racist Delph."
Dvorak said he does not believe the woman’s email poses an immediate threat to the senator or his staff.
"If it’s determined it constitutes a crime," Dvorak said, "action will be taken."
Staff writer Mary Kate Malone: