A symbol similar to one often left by the nefarious Zodiac killer of the 1960s was scrawled in lipstick on a mirror in the North Carolina hotel room where Army Spc. Megan Touma was found June 21, police said.

A letter sent to a local newspaper and published last week also contained the symbol, a circle with a cross through it.

"I will start using my role-model's signature," writes the author of the letter, which was posted on the Web site of the Fayetteville Observer.

The Zodiac killer was blamed for at least five slayings in California in the late 1960s but never caught.

Police questioned the letter's credibility, and believe the author's claim of being a serial killer was an attempt to mislead investigators and the media.

Meanwhile, the Army's criminal investigations unit is joining the effort to catch the killer of the pregnant Fort Bragg soldier, and a second autopsy will be performed.

Police in Fayetteville, N.C., said civilian and military detectives are now treating last month's death of Touma, 23, as a homicide, although they have not determined the cause.

Authorities have a person of interest in the case, a soldier the military has said is assigned to the Fort Bragg-based U.S. Army Special Operations Command.

"It made sense. We've been providing information and working with Fayetteville from the start," said Chris Grey, a spokesman for the Army's Criminal Investigation Command.

Touma, of Cold Spring, Ky., was found at a Fayetteville motel after a maintenance supervisor smelled a foul odor coming from a room with a "do not disturb" sign.

The dental specialist was seven months pregnant and had recently arrived from a base in Germany. She was temporarily assigned to the base's 19th Replacement Company, and would have eventually been assigned to work at a base dental clinic.

The Army took possession of her body last week, with plans to perform a second autopsy and additional tests.

Grey said the Army was already monitoring the city's investigation into Touma's death when it formally joined the effort to solve the case. Fayetteville police spokesman Lt. David Sportsman said the police are still leading the investigation, but Army investigators have "worldwide" access to soldiers and are better able to gather information in Germany.

"As this investigation has matured and because of the obvious link to the U.S. Army, it was expected that Army CID (criminal investigators) would eventually work this case jointly with our agency," Sportsman said in a statement.

There was no mention Monday in Sportsman's statement of a letter sent to The Fayetteville Observer.

Police said Monday that neither the state medical examiners nor the Armed Forces Institute of Pathology have determined Touma's cause of death.

The Associated Press contributed to this report.