Former preacher Clinton Don Simpson, who was accused of molesting 12 children at his miniature train track, has been killed in prison. He was 76 years old

A Texas preacher accused of molesting 12 children at his miniature train track has been killed in prison, authorities have revealed.

Clinton Don Simpson, 76, died from blunt force injuries to his head at the Tarrant County Jail in Fort Worth on Wednesday morning.

He was pronounced dead at 3.09am at John Peter Smith Hospital. His death has been ruled a homicide and another inmate is accused of killing him.

The Texas Ranger Division is investigating.

Simpson turned himself in to police in 2007 after he was accused of molesting 11 girls and one boy at the miniature train track station he ran in his backyard.

Simpson spent 10 years in state hospitals because he was found incompetent to stand trail. He was only recently found competent and returned to Tarrant County Jail.

He was meant to undergo independent evaluations and a competency hearing because his defense attorney claimed he was still incompetent, according to the Star-Telegram.

Simpson faced 10 counts of aggravated sexual assault of a child, one count of continuous sexual abuse of a child under 14, and two counts of indecency by fondling.

Following his arrest, Simpson - who had preached part-time for Haslet Church of Christ - confessed to police that he had sexually assaulted the 12 children.

Simpson owned and often hosted children's parties at 'Mr Don's Whistle Stop', the miniature train station and track that he built and operated from his backyard.

The miniature train traveled on more than 1,000ft of track and included an 'above ground tunnel' and a '200ft long bridge', according to his old website.

Simpson, 76, died from blunt force injuries to his head at the Tarrant County Jail (pictured) in Fort Worth on Wednesday morning. His death has been ruled a homicide

Authorities began investigating Simpson after parents claimed he assaulted their three-year-old daughter when she rode on the train with him at a birthday party.

A number of parents then came forward and reported the possibility that Simpson had 'inappropriately touched' their 'preschool-age' daughters, the Star-Telegram reported.

Police received more than 200 calls from concerned parents within a week after Simpson's arrest.

Parents of two of Simpson's victims filed a civil lawsuit against him in 2007, but it was dropped a year later because he was found incompetent to stand trial in the criminal cases.

The parents said they had become friends with Simpson and his wife Mary in October 2006 and that the couple encouraged them to come to Mr Don's Whistle Stop.

For the span of a year, the parents took their daughters to the train track. After Simpson was arrested, they learned their daughters had been sexually assaulted and that Simpson had also exposed himself to them.

The parents alleged in the lawsuit that they discovered Simpson had also 'engaged in similar sexual behavior' with children in the 1980s.

They claimed Mary, a leader in church and a teacher at a local school, knew about it.

Simpson was initially placed on house arrest, but was hospitalized in 2009. His last court hearing had been in 2014.