A lawsuit filed against Uber claiming that the ride-sharing company was to blame for the jailing of an Uber driver who is charged with murder is a hoax, the Kalamazoo County Sheriff's Office said on Thursday.

The Sheriff's Office said officials became suspicious of the suit, filed in the name of murder suspect Jason Dalton, who is currently jailed in Kalamazoo County, Michigan, after seeing the online filing. The online filing included a facsimile of the envelope used to send the suit, which had a Philadelphia, Pennsylvania, postmark.

"Our mail does not go Philadelphia. That raised a lot of suspicion right there," Pali Matyas, an undersheriff, said in an interview.

The envelope in court documents was not a jail envelope, the postage did not match what the county jail uses and the hand-written court filing did not match handwriting the office had on file of Dalton, Matyas said.

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Deputies spoke with Dalton on Thursday in jail.

"He said that he didn’t send it, and didn’t authorize it and he didn’t know who did," Matyas said, adding that Dalton's attorney also had no knowledge of the lawsuit.

"All of that translates into a hoax," he said.

U.S. District Court for the Eastern District of Michigan, where the lawsuit was filed, was informed by the sheriff's office that it found the suit to be a hoax. If the lawsuit is proven to be fraudulent, it may take some time to remove the hand-written filing from the court's online records system, court spokesman Rod Hansen said.

The online court records shows the filing on Tuesday of a two-page, handwritten lawsuit against Uber by a person claiming to be Dalton and saying, "I'm in prison because of Uber."

Dalton is charged with shooting eight people, killing six of them, over a five-hour period on Feb. 20 in between driving customers for the Uber car service in Kalamazoo, which is about 150 miles (240 km) west of Detroit. Police said last month that Dalton admitted to the shootings.

He faces 16 charges, including six of murder that can bring life in prison.