The leader of the St. Paul branch of the NAACP said Tuesday that his organization has started its own investigation into whether police used excessive force in the arrest of a 15-year-old boy at a church picnic over the weekend.

Jeff Martin said he has not yet spoken with the boy's mother, but confirmed that the NAACP has been in contact with St. Paul police officials regarding the arrest, part of which was captured on video by a bystander.

Martin said he has not seen the video — he intends to obtain a full copy — but has read news reports that allege the officer used profanity when talking to the boy's mother.

"From what I have seen, I think it warrants an investigation on our part," Martin said. "In any event, the officer did not act professionally, at a minimum."

The incident began around 12:20 p.m. Sunday, when St. Paul police were called by a man who said his 14-year-old son had been assaulted and robbed in Ryan Park.

Officer Joel Johnston picked up an 11-year-old boy accused of hitting the older boy with a stick, and cited him for assault before deciding to release him to his mother, Edna Waddle, who was at a nearby picnic, said Steve Linders, a St. Paul police spokesman.

While Johnston was talking with Waddle, her 15-year-old son, Tyree Tucker, started arguing with the officer and using profanity, Linders said. The officer attempted to arrest Tucker for disorderly conduct, but he tried to pull away, and at some point, the officer and teen fell to the ground, Linders said.

The video, which has been posted on YouTube, shows Johnston on top of Tucker, who is face down on the ground. He appears to be trying to pull the boy's hands behind his back as several people shout nearby. Eventually, Johnston handcuffs the boy, gets him to his feet and puts him in the back of a squad car.

In an interview Tuesday, Waddle said as Johnston gave her custody of her younger son he told her to "Get your [expletive] kid and get out of here" and "Look at you. You are up at the buffet table feeding your fat [expletive] … what type of mother are you?"

Waddle said her older son was sticking up for her when Johnston arrested him.

"I want him to pay for what he did," said Waddle, 45. "There has to be consequences because this is just sending out a mixed message. We teach our kids that 'You need to respect the police. The police are good people and they are there for you,' and then it's like the kids see this?"

Waddle said she plans to sue the department and wants Johnston fired.

Tucker said Tuesday that the officer slammed him into a tree and then forcibly held him to the ground, making it difficult for him to breathe.

"I don't think he should have done that," said Tucker, who is biracial. Waddle is white.

Alex Weston, who is a member of St. Paul Fellowship, Waddle's church, said he ran over and saw Tucker on the ground with the officer's knee on his torso and his arm around his neck.

"I didn't feel like there was justification for what was happening," said Weston, who recorded part of the incident on his cellphone.

Linders said Waddle was arrested on obstruction because she was trying to pull her son away while Johnston was trying to handcuff him. She was not charged.

He said St. Paul Police Chief Tom Smith is "aware of the concerns," adding that the officer's use of force will be reviewed.

Tonya Tennessen, the spokeswoman for Mayor Chris Coleman, said, "The mayor is confident that the chief's review will be thorough and that he will take appropriate disciplinary actions if facts determine it's appropriate."

Johnston has been with the department since 1994. He has been disciplined for several minor violations, but also has received numerous accolades, including seven medals of commendation.

The incident comes at a time when police-community relations across the country have been strained in the wake of several high-profile shootings of suspects by police and numerous protests against police use of force.

Meanwhile, Black Lives Matter St. Paul posted a statement Monday demanding Johnston be fired. In an interview Tuesday, Rashad Turner, the group's leader, said plans are in the works for "a big event" to protest the arrest and how Johnston acted.

"This is what we do. We want to try to be as proactive as we can, but sometimes, we have to be reactive," Turner said. "More people are understanding that until we come together as communities and force the change, change isn't going to come."

nicole.norfleet@startribune.com 612-673-4495

jim.walsh@startribune.com 651-925-5041