Rochester, MN (KROC AM News) -The Rochester Police Department is now offering a $5,000 reward for information in a recent murder.

An unknown killer shot 38-year-old Brandon Arndt in the head when he answered a knock on his door around 4:00 AM Sept 10th.

Arndt was living with his mother at a residence at Bob’s Trailer Park along Marion Rd. She is the one who heard the shot and called 911 after finding her son dead.

Police Capt. John Sherwin announced the reward Monday and also provided an update on the investigation, which he says has been going on 24/7 since the murder. Sherwin says investigators feel strongly that Arndt was “targeted” although it’s possible it was "the result of a mistake.” He says investigators are certain there are people who know the killer and/or know something about the killing. He appealed to them to “do the right thing” and come forward “to help bring the killer to justice.” Sherwin says Arndt was not involved in any criminal activity and was still feeling the effects of a kidney transplant in January.

Sherwin also released a letter from Arndt’s mother, which began, “I am totally devastated at the loss of my only son Brandon.” It goes on to describe her son as a person who “was always willing to help others.”

Sherwin is urging anyone with information that might be useful to contact the Rochester Police Department directly at (507)328-6800, or indirectly through Crime Stoppers at 1-800-222-TIPS. Tipsters through Crime Stoppers can remain anonymous and may be eligible for a cash reward if the information leads to a conviction in this case.

News update: Rochester woman arrested with a blood/alcohol level of .32.