A Tennessee man pleaded guilty Thursday to defrauding the charity he created to benefit the people of Newtown following the 2012 Sandy Hook Elementary School massacre.

Robert Bruce, 35, apologized in federal court in Hartford and acknowledged he used money from his 26.4.26 Foundation for personal expenses.

The Nashville man pleaded guilty to a single count of wire fraud and faces between eight and 18 months in prison under the terms of a plea agreement.

The foundation organized marathons in which runners raised money for each of the 26 miles they ran, dedicating each mile to one of the 26 victims of the December 2012 shootings.

Bruce gave $30,000 to a youth sports academy in Newtown, but prosecutors say he stole about $28,000.

Bruce told Judge Alvin Thompson that he started the foundation to "effectuate change" and said he was touched by the outpouring of goodwill.

He also told the court that he spent three months in an in-patient treatment center getting help for a substance-abuse problem, but said nothing excuses his conduct.

"I deeply regret what I did and the impact it had on other people," he said.

Bruce originally faced six counts after being charged in February 2015, about a year after authorities were contacted by Ryan Graney, a co-founder of the charity. She told them Bruce had failed to account for about $73,000 of the $103,000 they had raised.

The charity held its first marathon in Nashville a week after the shooting, with more than 1,000 participants raising $30,000. Another was held in New Hampshire in 2013. More than 1,400 runners raised about $22,000 for the foundation, organizers said. The charity also received donations from runners in other events and over the Internet.

The wire fraud charge stemmed from a single donation of $26 from a Connecticut woman.

Graney has said she noticed something was amiss when she discovered suspicious charges to the foundation's account, including $1,200 for paddleboards. She said she later found a picture of a new paddleboard on Bruce's Instagram page.

Graney said she confronted Bruce and he promised to meet her and go over the organization's finances. She said he never showed up and then cut off contact with her.

Graney has not been accused of any wrongdoing. She is currently involved with the family of Sandy Hook victim Victoria Soto, helping to run an annual road race that has raised thousands of dollars to fund scholarships for students studying to become educators.

"I am relieved that this ordeal is over," Graney said Thursday in a statement to The Associated Press. "I'm ready for this chapter to be completely closed. To the families of Sandy Hook, I will again apologize to you. What started out as an amazing movement crumbled into a shameful ending. I am thankful that the right thing was finally done."

Sentencing is scheduled for Aug. 30.