SEATTLE (AP) — Seattle's police oversight board said Friday it will investigate the arrest of a protester who was seriously injured during an arrest this week.

A lawyer for the man said officers slammed the man to the ground and he hit his head on the pavement hard.

The Seattle Office of Police Accountability launched an investigation “to determine whether the individual was subjected to excessive force,” the agency’s director Andrew Myerberg.

There have been frequent protests in the Northwest's largest city since George Floyd was killed by police in May.

Seven protesters were arrested Wednesday night for obstruction, pedestrian interference, property damage, resisting arrest, and assaulting an officer, police said.

A protester was hospitalized in critical condition Wednesday night after he stopped moving while being arrested. Seattle police initially said the 30-year-old man was being arrested on suspension of causing property damage when he experienced a “medical episode.” EMT-trained officers on the scene provide care until fire personnel took him to the hospital.

Police said on Thursday that “investigators have learned the subject’s medical episode was potentially related to a substance the subject had ingested prior to police contact.”

The man, Kel Murphy-Dunford, was upgraded to serious condition on Thursday and was in satisfactory condition on Friday, said Susan Gregg, a hospital spokesperson.

Murphy-Dunford's lawyer, Karen Koehler, told the Associated Press on Friday that police comments about what he might have ingested are speculation and “unverified information.”

“We have a number of eye witnesses that say he was tackled by police, he struck his head, additional police piled on top of him," she said. “They said he hit his head so hard that they heard his skull hit the pavement.”

“He ended up on a ventilator and unconscious,” she said.

They filed an investigation request with the Office of Police Accountability on Thursday night, she said.

Myerberg said the agency's investigation into the incident will include interviews, reviewing body camera and security videos, police reports and medical records.

On Thursday night two people were arrested on property damage and obstruction charges during demonstrations in Seattle.

The two protesters were arrested before 10 p.m. after “property destruction” was reported in the city’s Capitol Hill neighborhood. Police also said a small fire was set in front of the East Precinct later in the evening but was quickly extinguished.