Phoenix police said 29-year-old Matthew Egler was booked on one count of arson of an occupied structure.
In charging documents obtained by KPNX-TV in Phoenix, police said Egler has been a volunteer for the Maricopa County Democratic Party but was banned for behavioral reasons. Investigators say the fire was retaliation after being recently rejected as a volunteer again.
“We are deeply saddened and shocked by today’s news, but appreciate the swift action by law enforcement to ensure that the suspect is in custody," state and county Democratic leaders said in a statement.
A message left at a cellphone number listed for Egler's family was not immediately returned. It was not immediately known if he had an attorney to speak on his behalf.
Police in the charging documents also mention that Egler discussed starting the fire and his “discontentment” with county Democratic officials in a Twitter account.
A Twitter account with the handle “Valley Leader” shows several videos of a man who matches a mugshot of Egler released by the Maricopa County Sheriff's Office talking about carrying out the fire. The man also claims to be married to Ivanka Trump.
The blaze occurred early Friday in a business district a few miles north of downtown Phoenix. Investigators said evidence indicated it was an act of arson.
The building is the longtime home of both the state and county Democrats. The northern portion of the building, which houses the operations for Maricopa County Democrats, was a total loss, said Steven Slugocki, the county chair. Damage was less extensive in the state party’s portion of the building, he said.
The fire destroyed computers, tablets, phone-banking equipment, campaign literature and years of candidate and organizing information, Slugocki said. It also burned political memorabilia accumulated over decades, including campaign materials for John F. Kennedy, he said.
Arizona Republican Party leaders also condemned the fire.