They said Larsen admitted to sexually abusing a high school student from the time the victim was 15.
"These crimes spanned decades and affected children ages five to 15, when the abuse of each of the four minor victims began," County Attorney Brad Carlyon said in a statement.
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A former Winslow High School wrestling coach sentenced to six years in prison after pleading guilty to sex crimes with minors.
Larsen was indicted in last October on more than 20 counts of various sex crimes, mostly from the 1990s.
He pleaded guilty to sexual conduct with a minor, attempted sexual conduct with a minor and three counts of public sexual indecency to a minor.
Prosecutors said after serving his prison sentence, Larsen will be placed on supervised probation for 15 years, must register as a sex offender and perform 300 hours of community service.