Felony assault and witness tampering charges have been filed against a 24-year-old Mankato man who is accused of attempting to assault a drug informant in jail.

William Joseph Roalson pleaded guilty to a third-degree drug possession charge in August and was sentenced Monday. The new charges, filed Friday, stem from a Sept. 25 incident at the Blue Earth County Jail.

Roalson was arrested in June for selling cocaine to a Minnesota River Valley Drug Task Force agent the previous November, or seven months earlier. The drug deal was set up by the informant, who helped the agent buy about 4 grams of cocaine from Roalson for $220, according to court records.

The informant, who was also in jail, told jail staff that Roalson suspected he was the informant. He said he had talked to Roalson and thought they had worked things out.

However, when the informant was being checked out of the jail on Sept. 25, Roalson began arguing with the man and attempted to assault him, jail staff reported.

Two female jailers first told Roalson to go to his cell for a lockdown, but ended up locking down the entire section of the jail after Roalson refused, the criminal complaint said. One of the jailers also was knocked to the floor and injured, the complaint said, when they both attempted to restrain Roalson.

He allegedly broke away from the other jailer and took two swings at the informant before other jailers arrived and restrained him, the complaint said.

Roalson is charged with fourth-degree assault of a correctional employee and tampering with a witness, both felonies. An initial court appearance had not been scheduled Friday.

After pleading guilty to the drug charge, Roalson was placed on probation for 10 years with the conditions he serve 28 days in jail, complete treatment and pay a $2,000 fine.