FLINT (WWJ) – A Flint man who tried to “teach his daughter a lesson” by brutally slashing her boyfriend with a knife is facing at least 25 years in prison.

Forty-year-old Tmando Allen Denson was convicted Monday in Genesee County Court of assault with intent to do great bodily harm less than murder after severely beating his daughter’s boyfriend in October 2012.

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County Prosecutor David Leyton said the attack happened after Denson found his then-15-year-old daughter and her 17-year-old boyfriend in her bedroom and suspected they were engaging in sexual activities.

“While many fathers have an understandable desire to protect their daughters, this man’s actions went far beyond any reasonable approach,” Leyton said after the verdict was read. “Tmando Denson is a very violent man and there is absolutely no rationalization or comprehensible excuse for what he did to the victim in this case.”

According to court documents, the incident began when Denson went to investigate a loud noise he had heard coming from the second floor. Testimony during trial indicated that the young couple was half-naked when they heard Denson’s footsteps climbing the stairs. The daughter was able to quickly get dressed but her boyfriend was still naked from the waist down when Denson entered the bedroom, documents show.

Prosecutors say after Denson started beating his daughter’s boyfriend, he ordered the pair to strip naked and began taking pictures of them with his cell phone. Denson then ordered the boyfriend to stay put while he went downstairs and returned with two knives, one in each hand. Prosecutors say Denson stood over the cowering victim and began cutting his back, shoulders, and legs — leaving permanent disfiguring scars.

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After slicing the boyfriend with knives, Denson ordered him to kiss his boot — but just as the teen began to do so, Denson kicked him in the face, documents show. Denson then walked the dazed and bloody victim outside and told him he did all that to “teach his daughter a lesson.”

At trial, both Denson’s daughter and his wife testified on his behalf. His daughter even claimed she was being sexually assaulted by the victim, but it wasn’t enough to sway a jury.

“I commend the work of Assistant Prosecutor Barney Whitesman and officer-in-charge Jason Cate for their hard work on this case and for cutting through the defense argument that this man was simply trying to protect his teenage daughter,” Leyton said.

Included as similar acts evidence during the trial was Denson’s 2002 conviction in Wayne County for shooting someone with a gun over a $75 drug debt.

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As a four-time habitual felony offender, Denson faces a minimum of 25-years and up to life in prison when he’s sentenced on Feb. 20.