Two teenage roommates are accused of separate robberies near the University of Hawaii at Manoa this month.

One of them, 18-year-old Christopher Hilongo, has allegedly confessed to four other robberies in the area during September. He also agreed to testify against his roommate, 19-year-old Christian Marumoto, in a separate robbery case.

The two were arrested within a day of each other at their Ahe Street address.

At about 3:30 a.m. Oct. 13, a UH security guard was making his last round for the hour by the National Marine Fisheries Service building.

Hilongo allegedly grabbed the guard from behind and threatened to break the guard's neck if he did not give him money. Five people in the area witnessed the robbery but ran away when the guard yelled for help, according to court documents.

The guard was pushed into the bushes and choked while the suspect allegedly took a wallet, two silver rings and a silver bracelet, according to a police affidavit. Hilongo asked the guard to get into the fisheries building, police said. The guard said he could not get into the building, but asked the suspect to use his cell phone to call for another guard to gain entry.

The guard called his supervisor and used a code word for trouble, and police were called. The suspect fled before police arrived, according to a police affidavit. While the guard was on the phone, he recognized Hilongo through a sketch of the suspect posted on a door nearby.

Hilongo was identified through a photographic lineup and arrested later that evening. He has been charged with first-degree robbery and kidnapping.

The next day, his roommate, Marumoto, was arrested after Hilongo identified him as the alleged perpetrator of an earlier robbery, according to police. Hilongo stated he would testify against Marumoto.

At about 11:35 p.m. Oct. 5, a woman was walking on University Avenue near Dole Street when Marumoto allegedly pulled up in his vehicle, grabbed the woman in a headlock and punched her.

Marumoto took the woman's purse before fleeing and used her credit card at a nearby Aloha Island Mini Mart shortly after the robbery, according to police.

Marumoto has been charged with second-degree robbery, two counts of unauthorized possession of confidential information, two counts of fraudulent use of a credit card and two counts of third-degree identity theft.

Hilongo also allegedly confessed to four other robberies. They include a Sept. 15 attempted robbery and a robbery involving an Uzi-type weapon, both of which occurred near Kanewai Park.

He has been charged only in the Oct. 13 case, the city Prosecutor's Office said. Police are investigating his claims of his involvement in the earlier robberies.