Detectives are investigating whether a Marine charged with the brutal slaying of a pregnant colleague might have e-mailed authorities to ask about turning himself in while on the run in Mexico.

But Onslow County sheriff's officials cautioned Saturday they are not sure whether the March 30 e-mail that claimed to be from Cpl. Cesar Laurean is genuine. Among other concerns, it was sent with the wrong spelling of Laurean's name.

"I tend to think it's less than a 50 percent probability," said sheriff's Capt. Rich Sutherland. "It had no impact on him being apprehended."

Laurean was arrested in a small Mexican town on Thursday. He is charged with the December murder of Marine Lance Cpl. Maria Lauterbach, who had accused him of rape. He now faces an extradition process that will take at least 60 days, and maybe as long as a year or more, depending on whether he fights efforts to return him to the United States.

The e-mail was sent to Onslow County Sheriff Ed Brown. Sutherland said it appeared to have been sent from Mexico and was consistent with others authorities know he had sent while in hiding.

It read: "Sir, Can you assure immunity from a military court martial if I come back? , I know they will convict me with no evidence, I cant risk Leavenworth or a chain gang, what can you do for me?"

Laurean is charged with first-degree murder in civilian court. While the military could technically seek charges at the same time as civilian authorities, legal experts have said such a joint prosecution is not recommended by the military's manual for courts martial and happens rarely and only in unusual sets of circumstances.

Three days after receiving the e-mail, Brown replied. After telling Laurean that turning himself in would be the "wisest thing you could do," Brown answered his question about immunity.

"My answer, after consulting with District Attorney Dewey Hudson, I cannot assure you immunity from the military court; however, at this time it is the civilian authorities who have charged you and I understand the military is leaving everything up to the civilian authorities."

Police arrested Laurean, 21, of Las Vegas, as he was walking along the main street in San Juan de la Vina in the Mexican municipality of Tacambaro. He was born in Guadalajara but reportedly moved to the U.S. more than 10 years ago.

While in Mexico, Laurean communicated with his wife Christina using the MySpace social-networking service and repeatedly asked for help — which she refused. Hudson has said that evidence recovered from the computer Christina Laurean used allowed detectives to identify the Internet cafes in Mexico where Laurean was accessing the Internet.

Laurean and Lauterbach were assigned to the same logistics unit at Camp Lejeune, the expansive base on the North Carolina coast that is home to roughly 50,000 Marines. Authorities believe Laurean killed her in mid-December, and have said they found the burned remains of her body and those of her fetus in his backyard.