Three juveniles have been arrested and charged in connection with two recent violent assaults on Twin Cities light-rail trains.

Metro Transit police used surveillance video to track down the 16- and 17-year-old boys who are accused of beating one man and stealing a cellphone from another passenger the night of Dec. 4 on the Green Line in St. Paul. The suspects also are believed to have assaulted a Transportation Security Administration agent on the Blue Line in Minneapolis on Nov. 25, said Howie Padilla, a transit agency spokesman.

Police on Tuesday announced the arrest of a fourth suspect and said they have identified a total of six people who were involved with the attack in St. Paul.

“Investigators are also looking into other assaults to see if they can link these or any other cases together,” said Padilla, who encouraged others who may have been victims to report it. “We want to know about that.”

The arrests come as Metro Transit grapples with a recent spate of violence on Twin Cities public transportation, including on light-rail trains where serious crimes, such as robberies, aggravated assaults and theft, were up 35% through October compared with 2018. Metro Transit Police Chief Eddie Frizell, who took over as the agency’s top cop just five months ago, said he believes light-rail trains are safe, but concedes there has been an uptick in crime this year.

Frizell plans to have the department’s 141 full-time and 51 part-time officers walk or ride their beats in the coming weeks to address criminal behavior. He also plans additional outreach to business and community leaders — he met with some Tuesday — and using technology to track and analyze trends to fight crime.

In the St. Paul assault, seven juveniles boarded a westbound Green Line train near the Hamline Avenue Station around 9 p.m. and were loud and yelling profanities. The teens surrounded a man standing in the aisle and one of them started punching and kicking him repeatedly, according to charges filed in Ramsey County Juvenile Court. Two other suspects joined in to “kick, punch and stomp” the victim multiple times. One of the teens picked up the victim and slammed him onto the floor and another kicked him in the head as the man lay there, the charges said.

The victim was a “mild-mannered vulnerable adult” who had no interest in interacting with the suspects, the victim’s uncle said.

As the attack occurred, other passengers stepped up and told the teens to stop beating the man. The teens then punched and kicked one of the bystanders. One of the teens stole the bystander’s cellphone and attempted to take his bicycle before running off the train at the Snelling Avenue Station, the charges said.

A third man told police a group of juveniles punched him as he left the Culver’s restaurant on University Avenue, which is near the Snelling Avenue light-rail platform.

Police used a still photo from the train’s surveillance footage to identify seven suspects. Officers then spotted “six or seven” suspects inside the Culver’s. The teens ran out of the restaurant, but officers caught three of them, the charges said.

Victims identified the teens to police, the charges said.

One of the suspects told police that he boarded the train and saw “this dude mumbling something under his breath.” The teen told the man to speak up, and when the man did, the teen suspect “snapped and went off on him.” The two other suspects declined to speak with investigators, the charges said.

One of the suspects, who turned 17 on the night of the Green Line attack, was charged with two counts of aggravated robbery and fifth-degree assault inflicting or attempting bodily harm. Another 17-year-old was charged with the same offenses and a 16-year-old was charged with two counts of aggravated robbery.

Two of the suspects appeared in court Monday. The third is set to appear Dec. 17.

The charges were filed in juvenile court, but it’s possible the suspects could be charged as adults, said Dennis Gerhardstein, a spokesman for the Ramsey County Attorney’s Office.

Four teens involved in the Minneapolis attack in which suspects grabbed the victim’s hair and hit him in the head have yet to be charged, but cases against them have been sent to the Hennepin County Attorney’s Office, Padilla said.

All Metro Transit buses, trains and platforms are outfitted with cameras. Together with help from the public, police can catch those who commit crimes on public transportation, Padilla said.

“Let this be a warning to people who make these bad decisions: Don’t do it,” Padilla said.

Padilla said those who witness crimes can call 911 or remain anonymous by using Metro Transit’s Text For Safety feature. The agency recently expanded the hours the texting service is available. It now operates from 5 a.m. to 2 a.m. daily.

Staff writers Janet Moore and Ryan Faircloth contributed to this story. Tim Harlow • 612-673-7768

Correction: Previously versions of this article included a photo caption that misspelled the last name of Metro Transit police officer Erika Hatle.