An 18-year-old Oklahoma man who was already under investigation for the rape of a 14-year-old girl was arrested last month and charged with plotting the murder of another ex-girlfriend and her mother.

Matthew Austin reportedly told a witness he was angry at his ex-girlfriend who was “ruining his life” by refusing to drop a separate rape charge against him, KWTV reported.

The witness allegedly advised the teen not to try such a crazy plan, but he insisted that it was foolproof and that he planned to “just stab them so they wouldn’t scream.” The witness called police after he left, and officers found him near the ex-girlfriend’s house with a Home Depot bag containing a painter’s mask and latex gloves.

“I believe he initially gave the officers an excuse, like he wanted to paint his room or something like that,” said Norman police spokeswoman Sarah Schettler.

According to Law&Crime, Austin was arrested on July 18 and eventually confessed to his plans to kill his ex and her mother. He also told them that he was under investigation in Moore for the alleged rape of the 14-year-old girl and told them he believed she was 19. He was eventually charged with rape on August 1.

An arrest warrant says the investigation into Moore began on July 14, when the girl’s mother contacted police about the alleged rape. She showed officers text messages between Austin and the girl, beginning with their first encounter at the church. Police said Austin told the girl he was 16.

During a forensic interview, the victim said Austin “came to her apartment, forced himself on her and raped her,” the affidavit states. He told her “everything would be OK and not to tell anyone because they were old and it had to be a secret.”

He also told the victim “that he had done this before and that everything would be fine,” the affidavit states.

Bail for the rape is $400,000. In Norman, he is charged with planning a violent crime (bail $25,000) and plotting to cause serious bodily harm and intimidating witnesses (bail $5,000 each).

He was also charged with possession of a controlled substance and is being held in the Cleveland County Jail.

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(Featured image: Matthew Austin/Cleveland County Sheriff’s Office)