CENTENNIAL — Forsythia Eliese Owen was sentenced Friday to 38 years in prison for killing Denzel Rainey with a baseball bat in September 2013.

Rainey was savagely beaten to death by Owen, who had falsely accused him of sexually assaulting her child, in the early-morning hours while he slept in an alley.

Before the sentence was handed down, Owen’s attorney cited mental illness as a mitigating circumstance in the case. The prosecution, however, argued that Owen’s lack of concern — demonstrated by a pattern of refusal to medicate and, instead, self-treat by abusing marijuana and alcohol — made her mental illness an aggravating factor. The jury found Owen guilty of second-degree murder.

The night Owen murdered Rainey, she had been smoking marijuana and drinking with friends. She unjustly accused Rainey, whom she knew, of molesting her daughter.

Owen dismissed the counsel of friends, who told her to call police, and instead took the matter into her own hands.

She “engaged in misplaced, vigilante justice,” said Jason Siers, senior chief deputy district attorney in Arapahoe County.

Rainey was found bleeding profusely from multiple wounds to his head and body in an Englewood alley.

He was taken to a hospital, where he died a short time later.

Owen was arrested the day after the attack.

“Rainey was not guilty of any of those acts,” said District Judge Marilyn Leonard Antrim. “His memory should not be tarnished.”

Defense Attorney Joseph Archambault asked the court to sentence Owen to 16 years, the minimum; Siers argued for 48 years, the maximum.

Archambault said Owen has been taking medication since going to jail after her arrest, that she’s been in counseling and has a great desire to again be involved in her young child’s life.

Owen’s mental health issues (she was described in court as being bipolar) surfaced years ago when she stabbed a boyfriend in 2002, Siers said.

Owen was imprisoned for that attack but didn’t learn from it, Siers told the court.

Her violent, delusional behavior “escalated from a stabbing to a homicide,” Siers said. “Based on her history, I’m skeptical.”

Owen, dressed in a red jail jumpsuit and shackles, addressed the court.

In a voice shaky with emotion, Owen apologized for the “pain” she caused Rainey’s family and friends, as well the pain inflicted on her family and friends by her actions.

“I do know this is not acceptable,” she said of the fatal attack.

In handing down the 38-year sentence, Antrim noted that Owen is best behaved when she is in custody. Owen “prefers the siren call of drugs and alcohol” to prescription medication and counseling, Antrim said.

Antrim said she has concerns that Owen would, if free, “once again move to the sound of the siren song.”

After the sentence was announced, Owen turned to the gallery and said “I love you,” three times to supporters. A deputy leaned toward her and told Owen to face forward.

A short time later, she was led from the courtroom.

Kieran Nicholson: 303-954-1822, knicholson@denverpost.com or twitter.com/kierannicholson