The U.S. Army is launching an investigation into the October mass shooting perpetrated by a deranged reservist. 

U.S. Army officials announced Friday the investigation into Robert Card, a former Army reservist who killed 18 people in Lewiston, Maine, on Oct. 25.

"The Secretary of the Army has requested the Army Inspector General to conduct an independent investigation to ensure that the Army takes corrective actions where appropriate," reads a letter sent from Under Secretary of the Army Gabe Camarillo to Sen. Susan Collins.

MAINE SHOOTING: LEWISTON POLICE WERE WARNED ABOUT ROBERT CARD WEEKS BEFORE MASSACRE

Memorial for Maine shooting victims

Rain-soaked memorials for those who died sit along the roadside by Schemengees Bar & Grille in Lewiston, Maine. (AP Photo/Matt York)

"In response, the Army IG has instructed her team to immediately begin preparing to conduct this investigation," the letter to Collins reads. "The IG investigation will formally commence either upon cessation of the ongoing U.S. Army Reserve investigation or by February 1st 2024, whichever comes first."

Collins, along with fellow Maine Sen. Angus King, filed a letter to the Army Inspector General in November demanding a review of the events leading up to the tragedy.

Additionally, the state's congressional delegation filed a letter on Dec. 8 similarly demanding the inspector general "conduct an investigation separate from the ongoing administrative review conducted pursuant to the Army’s Suicide Prevention Program regulations."

LEWISTON, MAINE MASS SHOOTING: AT LEAST 22 DEAD AS MANHUNT INTENSIFIES FOR PERSON OF INTEREST ROBERT CARD

Susan Collins and Angus King walking

Maine Sens. Susan Collins and Angus King (Getty)

The congressional delegation reacted positively to the U.S. Army's announcement on Friday.

"We are pleased that the Inspector General of the Army has responded to our requests and has begun preparations to conduct an independent investigation into the events preceding the Lewiston shooting," the delegation said in a press release.

Card committed the October mass shooting in Lewiston at Schemengees Bar and Grille and the Just-In-Time Recreation bowling alley, which left 18 people dead and another 13 injured.

Robert Card is pictured

Robert Card, the gunman behind the Oct. 25 mass shooting in Lewiston, Maine. (Maine Department of Public Safety)

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Card was found dead as a result of an apparent self-inflicted gunshot wound near a dumpster at a recycling plant where he worked at one point in Lisbon, Maine.

Card was a trained firearms instructor who had reported mental health issues, including "hearing voices and threats to shoot up the National Guard Base in Saco, ME," according to a Maine law enforcement bulletin previously shared with Fox News Digital.