Updated

A man suspected in at least five killings in Missouri and Arkansas has pleaded guilty to charges that he strangled two women in St. Louis after doing drugs with them.

Theodis Hill, 50, entered the pleas Thursday and will be sentenced to life in prison without parole on July 10, the St. Louis Post-Dispatch reported. Hill admitted he killed 46-year-old Janice Mayhew in her apartment in 2008 and 22-year-old Sierra Sullivan at a St. Louis hotel in 2009.

It was only after Hill began writing letters to authorities while in prison for killing a woman in 2006 that investigators linked him to the additional homicides. Authorities say the letters contained details that only the killer would have known.

In a March letter to a St. Louis judge, Hill blamed the killings on what he said was his mental illness, claiming he was diagnosed with bipolar disorder, narcissistic personality disorder, and drug and alcohol dependence.

There's "something wrong with me to have committed 5 murders in two states and I feel it should be known that I'm not neglecting my responsibility," he wrote.

At that time, Hill was serving a 15-year term in Missouri for his admitted 2006 strangulation of 56-year-old Fanny Mae Hill, who is unrelated to Theodis Hill. While imprisoned, Hill pleaded guilty to killing 40-year-old Marissa Lowe in 2009 in Forrest City, Arkansas, where he apparently went to help relatives fix up a home. He was sentenced to 40 additional years in that case.

While in prison, Hill wrote to an Arkansas prosecutor in early 2014, admitting he suffocated another woman — Katherine Dawson, 48 — with a pillow in the Forrest City area about two weeks before Lowe's body was found. He now awaits trial on a murder charge related to Dawson's death.

___

Information from: St. Louis Post-Dispatch, http://www.stltoday.com