The Ramsey County sheriff's deputy who fatally shot a Twin Cities man last year after a struggle inside an RV will not face criminal charges.

The Ramsey County Attorney's Office announced Thursday that it would not pursue charges against deputy Andre Rongitsch or the three other officers who were present when he shot Darren Jahnke.

"I guess I had prayed that it would be different, but I know the history of these types of cases," said Jahnke's sister, Jenny Vance. "I guess I wasn't extremely shocked [with the decision], but I was very disappointed."

An e-mail written by Ramsey County Attorney John Choi to his staff said that Jahnke had put a deputy's life in danger.

"Deputy Lisa Daly was fighting for her life after she was tackled to the ground by Darren Jahnke," said the e-mail. "Based upon his training and the situation at hand, Deputy Andre Rongitsch had no other course of action other than to fire his weapon, which he did as a last resort to stop the immediate threat that was posed to Deputy Daly."

Jahnke, 47, was shot April 16 inside an RV parked in the 3200 block of Fanum Road in Vadnais Heights. He died from a single gunshot to the back of the head.

A memo written by First Assistant Ramsey County Attorney John Kelly and Rick Dustherhoft, the office's adult criminal division director, said that deputies were investigating a sexual assault reported on April 13 when they encountered Jahnke sitting in the driver's seat of an RV. The assault had occurred in a similar RV at a different location in nearby Little Canada.

According to the memo: Jahnke, who had a warrant out for his arrest for probation violation, declined to identify himself during 22 minutes of questioning.

"You have no legal right to ask me," he allegedly told Rongitsch and Daly.

The deputies forced their way into the RV when Jahnke refused to surrender. He allegedly threatened the deputies with a bucket of feces and then ripped Daly's gun off her belt before he was shot.

Daly suffered injuries and Jahnke's DNA was found on her gun, Kelly and Dusterhoft wrote.

Teresa Nelson, legal director of the American Civil Liberties Union of Minnesota, reviewed the memo and said the deputies acted within the law in questioning Jahnke, but she questioned whether they could have de-escalated the situation.

"At a minimum, they had enough level of suspicion to do what is known as … a stop for questioning," she said. "I'm concerned any time officers are escalating a situation. And the question that I have is, 'Was this necessary? Could they have found a better way to deal with the situation?' "

Authorities later learned that several people had access to the RV, that Jahnke and his girlfriend had been living out of a car and that he went to help a friend fix the RV on April 15.

Ramsey County Sheriff Jack Serier said that the department would now begin its internal review of the incident, which also involved deputies Doug Haider and Sara Naglosky.

Vance said that an independent autopsy commissioned by the family was scheduled to take place Thursday. She said she had no updated information about the autopsy.

"I really don't know what I hope to find," she said. "I just want to know something."