A 16-year-old already facing armed robbery and kidnapping charges for two incidents on Jan. 13 was arraigned yesterday on new charges of armed robbery, kidnapping and indecent assault and battery for incidents on Jan. 11 and 13, the Suffolk County District Attorney's office reports.

The teen, not named because of his age, had his bail increased from $1 million to $2 million in Dorchester Municipal Court due to the new charges, the DA's office reports. Although he gave his last address as a school in Lancaster, he has family in Dorchester.

The DA's office described the four incidents:

Around 10 p.m. on Jan. 11, he robbed another teen of his phone at the Fields Corner Red Line station.

Around midnight on Jan. 13, he followed a woman from Fields Corner to Neponset Avenue, then "stuck what she believed to be a gun in her back, and ordered him to return with him to Fields Corner. The woman escaped by suggesting they walk along Gibson Street - which she knew was home to the Boston Police C-11 district station. She bolted away from him, ran into the station."

Around 12:25 a.m., he hopped on the Red Line, prosecutors say. He "allegedly grasped a handgun-like object in his jacket pocket, demanded a woman's iPhone while riding the Red Line inbound between Savin Hill and Andrew stations, then tried unsuccessfully to drag her off the train."

About 20 minutes after that, the DA's office reports, "the juvenile allegedly assaulted an adult female at Fields Corner, put what she believed to be a gun to her back, and brought her to a nearby location where he sexually assaulted her and took her purse, containing an iPhone and identification cards.

All of his victims were able to give police detailed descriptions, down to the red and white bandana he carried or wore in the Jan. 13 attacks. Transit Police were able to pull up images of him from surveillance cameras around Fields Corner. When they heard Boston Police were investigating new attacks two days later, they shared their information.

"Just a few hours after the last attack on Jan. 13, Transit Police observed footage of the juvenile, wearing clothing consistent with the unknown assailant, at Fields Corner," the DA's office reports. "Transit Police immediately responded to the area and ordered all trains held at the station. The juvenile was not on scene when the first officers arrived, but they soon located him at a nearby McDonalds on Dorchester Avenue."

"The officers recovered a replica handgun from the juvenile's waistband. At the time of his arrest, he was wearing a red hooded sweatshirt, a black vest, red-and-black sneakers, and a pair of red pants underneath a pair of black pants. In his possession were a bandanna, a bank card and iPhone belonging to the sexual assault victim, and another iPhone belonging to the woman robbed on the Red Line train."