McINTOSH COUNTY, Oklahoma - Investigators believe they may have prevented a mass shooting in Green Country after arresting a man they said posted threats on Facebook to shoot up the McIntosh County Courthouse in Eufaula today.

They said in light of the dozens killed just this weekend in El Paso and Dayton, they had to take this threat seriously and people from several agencies worked through the night to make the arrest.

Investigators said Shane Hammer made a goodbye post to his friends and said the next time they'd see him is on the media because he's ready to go to war. They said he was asking for others to join him here at the courthouse and he told his friends he wouldn't stop until he was killed.

"I’m looking for some riders that will go to war with me tomorrow" Hammer said in a post. "Tomorrow at 2 p.m., I got the tool to do this."

Hammer also said, "all I can say is I'm ready for war, I will not stop until I get killed."

He referred to his court case, as the case from hell.

Carol Iski, McIntosh County DA says, "This could've been really bad."

She credits her two investigators Andy Blizzard and Keven Branscum along with the FBI Safe Trails Task Force, Tahlequah police and the McIntosh County Sheriff’s office with moving quickly once the tip from a citizen came in to track Hammer to an area in Cherokee County and make the arrest.

Iski says, "We took fast action."

She said Hammer has a history of violence, has been to prison, and is currently on probation for being a felon with a gun and threatening to kill a DHS worker.

Iski said, "since just a few days ago, we had shootings in two different cities. Certainly, it's something we don't take lightly."

About 50 people work inside the courthouse and employees said the hallway, where Hammer was supposed to be in court, would've been packed with people.

The employees said they're grateful for the citizen who spoke up and how law enforcement worked together.

Assessor Trina Williams said even though they’ve added security to the courthouse and had safety meetings, her staff works in the office right inside the front door, which is could be a prime target.

“We'll be the first people if someone comes in shooting," Williams said.

The DA said she is now trying to decide exactly what charges Hammer will face and if he's going to face them in state court or perhaps, federal court.