JEFFERSON CITY, Mo. -- The U.S. Army has assigned a senior colonel to investigate whether state Sen. Jon Dolan violated any military regulations by returning on leave to Missouri to cast the deciding vote enacting a concealed-guns law.

While the officer's involvement signifies an increased interest in Dolan's case, the Army has stopped short of launching a formal investigation, which would include judicial-style proceedings, Raul Duany, a spokesman for the U.S. Army's Southern Command, said Friday.

The Army colonel, whom Duany declined to identify, was dispatched Monday from command headquarters in Miami to Guantanamo Bay, Cuba, where Dolan is assigned as a public affairs major through the Missouri Army National Guard.

Dolan, a Republican from Lake St. Louis, said in an e-mail Tuesday to The Associated Press that he had just completed his interview as part of the investigation being conducted under Army Regulation 15-6.

That regulation allows for either informal or formal investigations. Informal investigations, such as Dolan's, usually have a single investigating officer who conducts interviews and collects evidence. Sworn statements are not necessarily required but are an option, and are being used in Dolan's case, Duany said.

"It's sort of an administrative process (in which) we're looking at the circumstances and facts as far as who granted the leave, and why, and who knew what," Duany said.

Unlike a formal investigation, usually headed by a panel of people, there are no due process proceedings in informal investigations, meaning the investigator does not have subpoena power and no one is entitled to be represented by an attorney or to call and cross-examine witnesses.

Although there is no deadline to complete an informal investigation, Duany said they typically are wrapped up in three weeks. Dolan said he expects to know more about the results of the investigation in a week or two.

The investigating colonel is to submit recommendations to officials at the Southern Command, who then would decide what, if any, action to take.

Among the military rules at issue in the investigation is one stating that reserve officers shall not "hold or exercise the functions of civil office" while on active military duty "under a call or order for a period in excess of 270 days."

Dolan is serving under a full-year active duty call, but had been on duty for just a couple of weeks when he was granted leave and returned Sept. 11 to the Senate to vote to override Holden's veto of a bill allowing Missourians to carry concealed guns. Dolan's votes also helped override vetoes on an abortion bill and a bill barring governments from suing the gun industry over the social costs of gun violence.

Dolan contends the rule only bars from political activity those active duty soldiers who already have served more than 270 days. But the Defense Department has said the rule affects anyone called to active duty for that long.

Dolan has hired a Virginia lawyer who specializes in military law. If the Army recommends a significant punishment or a court-martial, Dolan wants to be in a position to fight the charges, said Trent Watson, his Senate chief of staff.