The Princeton man accused of killing his younger brother appeared in person at Mercer County Court this morning.

News 12 was in the courtroom for Matthew Hertgen's hearing, where he voluntarily consented to be detained, with seven days to appeal that decision.

Hertgen is charged with first-degree murder in addition to several other charges in the killing of his younger brother, Joe Hertgen.

An affidavit from the Mercer County Prosecutor's Office shares details from the night and information leading up to the 911 call. In the document, a third Hertgen brother says he was with Matthew Hertgen earlier on the evening of Feb. 22, sharing that Matthew Hertgen had suffered from severe mental illness for the past five years and was extremely distressed, despondent and experiencing terrifying visions that Saturday.

Later that night, the third brother texted Joe Hertgen, warning Matthew Hertgen was struggling with his visions and to contact him immediately if he needed help. Joe Hertgen responded with "will do" and invited the brother to a hike the next day around 10:30 p.m. About 45 minutes later, Matthew called 911 and reported Joe dead, telling police he "went into a fit of madness."

The judge said the next court appearance will be on March 24.